From 2c08c53ef20984929dd16b7f6b1478fd7a5162f0 Mon Sep 17 00:00:00 2001
From: Andreas Stefl <stefl.andreas@gmail.com>
Date: Wed, 26 Aug 2026 20:58:59 +0200
Subject: [PATCH 1/2] feat(html): let a host put a floor under the margin a
 view keeps
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

`HtmlConfig::min_content_margin` states, per side, the least distance the
generated content keeps from the view's border. Every view already insets
its content by some amount it names itself — 3mm for a reflowed text
document, 16px for the page column and the source views, 8px for a font
specimen, nothing for an image or a file listing — and no single number
could stand in for all of them, so the config is a floor rather than a
value: an unset side leaves the view exactly where it was, a set one only
ever raises it.

The arithmetic is css's. Each inset becomes `max(own, var(--odr-min-margin-*,
0px))`, so the view's own measure stays in the stylesheet and no unit has to
be converted to state it. `write_content_margin_style` declares the variables
per view and writes nothing at all when no side is set, which is what keeps
the shipped stylesheets independent of the config — they are shared under one
name when the config links rather than embeds them.

One place still needs the number: the gutter around the page column is part
of the width the view is fitted to, so `page_column_gutter_pixels` reads the
config and a side css can read but `css_pixels` cannot convert keeps the
built-in gutter — the margin still applies, only the fit cannot count it. A
unit css could not read at all is dropped rather than written into the style
element it would otherwise close.

A sheet and the media view are not inset: the one meets the edge by design,
the other is full-bleed.

Bound in python, jni, wasm (`minContentMargin`, css lengths as strings) and
apple, where `ODRMeasure` and `ODRDirectionalMeasure` gain the initialisers a
caller needs to state one.

Rendering with the default config is unchanged. Where the stylesheet is linked
the document is byte-identical; where it is embedded — the image, pdf and font
views — the reference output restates the same insets as `max(own, var(...))`,
which with the variables unset is the number it always was, and the shipped
stylesheets render pixel-identically under `compare-html`. The reference-output
pins are advanced to match.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UoWywNazPio5vphzB59U5g
---
 CHANGELOG.md                                  |  7 ++
 apple/include/OdrCoreObjC/ODRHtml.h           |  6 ++
 apple/include/OdrCoreObjC/ODRStyle.h          | 12 ++++
 apple/src/ODRHtml.mm                          |  7 ++
 apple/src/ODRPrivate.h                        |  4 ++
 apple/src/ODRStyle.mm                         | 44 ++++++++++++
 apple/tests/OdrCoreTests.swift                | 20 ++++++
 .../app/opendocument/core/HtmlConfig.java     |  7 ++
 jni/src/jni_style.cpp                         | 46 ++++++++++++
 jni/tests/app/opendocument/core/HtmlTest.java | 20 ++++++
 python/src/bind_html.cpp                      |  1 +
 python/tests/test_html.py                     | 23 ++++++
 src/odr/html.hpp                              |  9 +++
 src/odr/internal/html/common.cpp              | 67 +++++++++++++++++
 src/odr/internal/html/common.hpp              | 15 +++-
 src/odr/internal/html/document.cpp            | 55 ++++++++------
 src/odr/internal/html/filesystem.cpp          |  1 +
 src/odr/internal/html/font_file.cpp           |  6 +-
 src/odr/internal/html/frontend.cpp            | 17 ++---
 src/odr/internal/html/image_file.cpp          |  7 +-
 src/odr/internal/html/pdf_file.cpp            | 19 +++--
 src/odr/internal/html/text_file.cpp           |  1 +
 src/odr/internal/html/xml_file.cpp            |  1 +
 test/data.cmake                               |  4 +-
 test/src/html_test.cpp                        | 72 +++++++++++++++++++
 wasm/js/index.d.ts                            | 11 +++
 wasm/src/wasm_html.cpp                        | 19 +++++
 wasm/tests/render.test.mjs                    | 20 ++++++
 28 files changed, 480 insertions(+), 41 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7847b6190..4eeedd26c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,13 @@ The release run heads these entries with the version and opens a fresh
 
 ## Unreleased
 
+- `HtmlConfig::min_content_margin` puts a floor under the distance the
+  generated content keeps from the view's border, per side. Unset, every view
+  keeps the inset it has today; a set side raises it - in a reflowed text
+  document, the page column of a text, presentation, drawing or pdf view, the
+  text and xml source views, the file listing, the image view and the font
+  specimen. A sheet and the media view are not inset. Bound in python, jni,
+  wasm (`minContentMargin`, css lengths as strings) and apple.
 - **Breaking** Bytes that do not read as text no longer come back as
   `text_file` and render as nonsense - `decode` throws `UnknownFileType` and
   `list_file_types` comes back empty. A file is text when it is empty, or its
diff --git a/apple/include/OdrCoreObjC/ODRHtml.h b/apple/include/OdrCoreObjC/ODRHtml.h
index 5f0bcf59e..ab6227ba5 100644
--- a/apple/include/OdrCoreObjC/ODRHtml.h
+++ b/apple/include/OdrCoreObjC/ODRHtml.h
@@ -1,6 +1,7 @@
 #import <Foundation/Foundation.h>
 
 #import <OdrCoreObjC/ODRFilesystem.h>
+#import <OdrCoreObjC/ODRStyle.h>
 #import <OdrCoreObjC/ODRTable.h>
 
 NS_ASSUME_NONNULL_BEGIN
@@ -101,6 +102,11 @@ NS_SWIFT_NAME(HtmlConfig)
 /// The zoom the view opens at, 1 being actual size; `nil` follows the fit.
 @property(nonatomic, strong, nullable) NSNumber *initialZoom;
 
+/// The least distance the generated content keeps from the view's border. A
+/// `nil` side keeps the inset the view already has; a set side raises it,
+/// never lowers it.
+@property(nonatomic, strong) ODRDirectionalMeasure *minContentMargin;
+
 @property(nonatomic) BOOL formatHtml;
 /// Repeated `htmlIndentString` per nesting level; 0 disables indentation.
 @property(nonatomic) uint8_t htmlIndent;
diff --git a/apple/include/OdrCoreObjC/ODRStyle.h b/apple/include/OdrCoreObjC/ODRStyle.h
index 99f8c7a8c..668b75d0e 100644
--- a/apple/include/OdrCoreObjC/ODRStyle.h
+++ b/apple/include/OdrCoreObjC/ODRStyle.h
@@ -79,6 +79,11 @@ NS_SWIFT_NAME(Measure)
 /// Magnitude and unit as odrcore writes them, e.g. `12pt`.
 @property(nonatomic, readonly, copy) NSString *stringValue;
 
+/// A css length as odrcore writes one, e.g. `3mm`. A magnitude with no unit
+/// reads as unitless.
+- (instancetype)initWithString:(NSString *)string;
+- (instancetype)initWithMagnitude:(double)magnitude unit:(NSString *)unit;
+
 - (instancetype)init NS_UNAVAILABLE;
 + (instancetype)new NS_UNAVAILABLE;
 @end
@@ -92,6 +97,13 @@ NS_SWIFT_NAME(DirectionalMeasure)
 @property(nonatomic, readonly, nullable) ODRMeasure *left;
 @property(nonatomic, readonly, nullable) ODRMeasure *bottom;
 
+/// For the sides a caller states itself, e.g.
+/// @ref ODRHtmlConfig.minContentMargin.
+- (instancetype)initWithRight:(nullable ODRMeasure *)right
+                          top:(nullable ODRMeasure *)top
+                         left:(nullable ODRMeasure *)left
+                       bottom:(nullable ODRMeasure *)bottom;
+
 - (instancetype)init NS_UNAVAILABLE;
 + (instancetype)new NS_UNAVAILABLE;
 @end
diff --git a/apple/src/ODRHtml.mm b/apple/src/ODRHtml.mm
index 32c512f96..7f6a06d8e 100644
--- a/apple/src/ODRHtml.mm
+++ b/apple/src/ODRHtml.mm
@@ -108,6 +108,8 @@ - (instancetype)initWithNativeConfig:(const odr::HtmlConfig &)config {
   _viewportContent = config.viewport_content.has_value()
                          ? to_nsstring(*config.viewport_content)
                          : nil;
+  _minContentMargin =
+      [ODRDirectionalMeasure directionalWithHandle:config.min_content_margin];
   _viewportWidth = config.viewport_width.has_value()
                        ? @(static_cast<unsigned int>(*config.viewport_width))
                        : nil;
@@ -187,6 +189,11 @@ - (instancetype)initWithNativeConfig:(const odr::HtmlConfig &)config {
   } else {
     config.initial_zoom.reset();
   }
+  if (_minContentMargin != nil) {
+    config.min_content_margin = _minContentMargin.handle;
+  } else {
+    config.min_content_margin = odr::DirectionalStyle<odr::Measure>();
+  }
   config.format_html = _formatHtml == YES;
   config.html_indent = _htmlIndent;
   config.html_indent_string = to_string(_htmlIndentString);
diff --git a/apple/src/ODRPrivate.h b/apple/src/ODRPrivate.h
index 85affbc68..295aaaeca 100644
--- a/apple/src/ODRPrivate.h
+++ b/apple/src/ODRPrivate.h
@@ -17,6 +17,8 @@
 #include <odr/logger.hpp>
 #include <odr/style.hpp>
 
+#include <optional>
+
 /// Cross-translation-unit access to the C++ value each wrapper owns.
 ///
 /// Each `@implementation` holds its handle as an ivar, destroyed by ARC's
@@ -85,11 +87,13 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface ODRMeasure (Private)
 + (instancetype)measureWithHandle:(const odr::Measure &)handle;
+- (const std::optional<odr::Measure> &)handle;
 @end
 
 @interface ODRDirectionalMeasure (Private)
 + (instancetype)directionalWithHandle:
     (const odr::DirectionalStyle<odr::Measure> &)handle;
+- (odr::DirectionalStyle<odr::Measure>)handle;
 @end
 
 @interface ODRDirectionalString (Private)
diff --git a/apple/src/ODRStyle.mm b/apple/src/ODRStyle.mm
index b233407ad..fca09ff4b 100644
--- a/apple/src/ODRStyle.mm
+++ b/apple/src/ODRStyle.mm
@@ -9,6 +9,7 @@
 
 using odr::apple::guarded_value;
 using odr::apple::to_nsstring;
+using odr::apple::to_string;
 
 ODR_SAME_ENUM(ODRFontWeightNormal, odr::FontWeight::normal);
 ODR_SAME_ENUM(ODRFontWeightBold, odr::FontWeight::bold);
@@ -107,6 +108,26 @@ - (NSString *)stringValue {
   return guarded_value([&] { return to_nsstring(_handle->to_string()); }, @"");
 }
 
+- (instancetype)initWithString:(NSString *)string {
+  if ((self = [super init]) == nil) {
+    return nil;
+  }
+  _handle = odr::Measure(to_string(string));
+  return self;
+}
+
+- (instancetype)initWithMagnitude:(double)magnitude unit:(NSString *)unit {
+  if ((self = [super init]) == nil) {
+    return nil;
+  }
+  _handle = odr::Measure(magnitude, odr::DynamicUnit(to_string(unit)));
+  return self;
+}
+
+- (const std::optional<odr::Measure> &)handle {
+  return _handle;
+}
+
 - (NSString *)description {
   return self.stringValue;
 }
@@ -127,6 +148,29 @@ + (instancetype)directionalWithHandle:
   return result;
 }
 
+- (instancetype)initWithRight:(ODRMeasure *)right
+                          top:(ODRMeasure *)top
+                         left:(ODRMeasure *)left
+                       bottom:(ODRMeasure *)bottom {
+  if ((self = [super init]) == nil) {
+    return nil;
+  }
+  _right = right;
+  _top = top;
+  _left = left;
+  _bottom = bottom;
+  return self;
+}
+
+- (odr::DirectionalStyle<odr::Measure>)handle {
+  odr::DirectionalStyle<odr::Measure> result;
+  result.right = _right != nil ? _right.handle : std::nullopt;
+  result.top = _top != nil ? _top.handle : std::nullopt;
+  result.left = _left != nil ? _left.handle : std::nullopt;
+  result.bottom = _bottom != nil ? _bottom.handle : std::nullopt;
+  return result;
+}
+
 @end
 
 @implementation ODRDirectionalString
diff --git a/apple/tests/OdrCoreTests.swift b/apple/tests/OdrCoreTests.swift
index 5facde83e..eccdee02f 100644
--- a/apple/tests/OdrCoreTests.swift
+++ b/apple/tests/OdrCoreTests.swift
@@ -119,6 +119,26 @@ final class HtmlTests: XCTestCase {
     XCTAssertTrue(html.contains("<style"), "the html has no stylesheet")
   }
 
+  /// The C++ suite covers where the floor lands; this only proves the margin
+  /// crosses the binding, `nil` sides and all.
+  func testMinContentMarginReachesTheHtml() throws {
+    let config = HtmlConfig()
+    config.minContentMargin = DirectionalMeasure(
+      right: nil, top: Measure(string: "12px"), left: Measure(string: "1cm"),
+      bottom: nil)
+
+    let file = try DecodedFile.decode(path: try Fixture.odt())
+    let service = try HtmlTranslator.translate(
+      file: file, cachePath: try temporaryDirectory(), config: config)
+    var resources: NSArray?
+    let html = try XCTUnwrap(service.views.first).writeHtml(resources: &resources)
+
+    XCTAssertTrue(
+      html.contains(":root{--odr-min-margin-top:12px;--odr-min-margin-left:1cm;}"),
+      "the margin did not reach the html")
+    XCTAssertFalse(html.contains("--odr-min-margin-right:"), "an unset side was written")
+  }
+
   /// A view's impl points into its service without owning it, so the view has
   /// to keep the service alive itself — the analogue of
   /// `ElementTreeTests.testElementsKeepTheirDocumentAlive`. Rendering off a
diff --git a/jni/java/app/opendocument/core/HtmlConfig.java b/jni/java/app/opendocument/core/HtmlConfig.java
index 116a0d174..699ab8ce3 100644
--- a/jni/java/app/opendocument/core/HtmlConfig.java
+++ b/jni/java/app/opendocument/core/HtmlConfig.java
@@ -42,6 +42,13 @@ public final class HtmlConfig {
   /** The zoom the view opens at, 1 being actual size; {@code null} follows the fit. */
   public Double initialZoom;
 
+  /**
+   * The least distance the generated content keeps from the view's border. A {@code null} side
+   * keeps the inset the view already has; a set side raises it, never lowers it.
+   */
+  public DirectionalMeasure minContentMargin =
+      new DirectionalMeasure(null, null, null, null);
+
   public boolean formatHtml = false;
   public int htmlIndent = 1;
   public String htmlIndentString = "\t";
diff --git a/jni/src/jni_style.cpp b/jni/src/jni_style.cpp
index a8fd74fff..11351acfb 100644
--- a/jni/src/jni_style.cpp
+++ b/jni/src/jni_style.cpp
@@ -173,6 +173,44 @@ make_directional_measure(JNIEnv *env,
       make_measure(env, style.left), make_measure(env, style.bottom));
 }
 
+std::optional<odr::Measure> measure_from_java(JNIEnv *env, jobject value) {
+  if (value == nullptr) {
+    return std::nullopt;
+  }
+  jclass cls = env->GetObjectClass(value);
+  const double magnitude =
+      env->GetDoubleField(value, env->GetFieldID(cls, "magnitude", "D"));
+  auto unit = static_cast<jstring>(env->GetObjectField(
+      value, env->GetFieldID(cls, "unit", "Ljava/lang/String;")));
+  const odr::Measure result(magnitude, odr::DynamicUnit(to_string(env, unit)));
+  env->DeleteLocalRef(unit);
+  env->DeleteLocalRef(cls);
+  return result;
+}
+
+odr::DirectionalStyle<odr::Measure>
+directional_measure_from_java(JNIEnv *env, jobject value) {
+  odr::DirectionalStyle<odr::Measure> result;
+  if (value == nullptr) {
+    return result;
+  }
+
+  jclass cls = env->GetObjectClass(value);
+  const auto side = [&](const char *name) {
+    jobject measure = env->GetObjectField(
+        value, env->GetFieldID(cls, name, "Lapp/opendocument/core/Measure;"));
+    std::optional<odr::Measure> parsed = measure_from_java(env, measure);
+    env->DeleteLocalRef(measure);
+    return parsed;
+  };
+  result.right = side("right");
+  result.top = side("top");
+  result.left = side("left");
+  result.bottom = side("bottom");
+  env->DeleteLocalRef(cls);
+  return result;
+}
+
 jobject
 make_directional_string(JNIEnv *env,
                         const odr::DirectionalStyle<std::string> &style) {
@@ -374,6 +412,8 @@ jobject html_config_to_java(JNIEnv *env, const odr::HtmlConfig &config) {
              box_integer(env, config.viewport_width));
   set_object("initialZoom", "Ljava/lang/Double;",
              box_double(env, config.initial_zoom));
+  set_object("minContentMargin", "Lapp/opendocument/core/DirectionalMeasure;",
+             make_directional_measure(env, config.min_content_margin));
   set_boolean("formatHtml", config.format_html);
   set_int("htmlIndent", config.html_indent);
   set_string("htmlIndentString", config.html_indent_string);
@@ -540,6 +580,12 @@ odr::HtmlConfig html_config_from_java(JNIEnv *env, jobject config) {
     }
     env->DeleteLocalRef(zoom);
   }
+  {
+    jobject margin = get_object("minContentMargin",
+                                "Lapp/opendocument/core/DirectionalMeasure;");
+    result.min_content_margin = directional_measure_from_java(env, margin);
+    env->DeleteLocalRef(margin);
+  }
   result.format_html = get_boolean("formatHtml");
   result.html_indent = static_cast<std::uint8_t>(get_int("htmlIndent"));
   result.html_indent_string = get_string("htmlIndentString");
diff --git a/jni/tests/app/opendocument/core/HtmlTest.java b/jni/tests/app/opendocument/core/HtmlTest.java
index 71ffaa9d9..fd33ff5ae 100644
--- a/jni/tests/app/opendocument/core/HtmlTest.java
+++ b/jni/tests/app/opendocument/core/HtmlTest.java
@@ -62,6 +62,26 @@ void viewportConfigRoundTrips() throws IOException {
     assertEquals(Double.valueOf(1.5), readBack.initialZoom);
   }
 
+  /** The C++ suite covers where the floor lands; this only proves it crosses JNI. */
+  @Test
+  void minContentMarginReachesTheHtml() throws IOException {
+    assertNull(new HtmlConfig().minContentMargin.top);
+    assertTrue(!renderOdt(new HtmlConfig()).contains(":root{--odr-min-margin"));
+
+    HtmlConfig config = new HtmlConfig();
+    config.minContentMargin =
+        new DirectionalMeasure(null, new Measure(12, "px"), new Measure(1, "cm"), null);
+    assertTrue(
+        renderOdt(config).contains(":root{--odr-min-margin-top:12px;--odr-min-margin-left:1cm;}"));
+
+    Path cache = Files.createDirectories(tempDir.resolve("margin"));
+    DecodedFile file = Odr.open(TestFiles.odtFile(tempDir).toString());
+    HtmlConfig readBack = Html.translate(file, cache.toString(), config).config();
+    assertEquals(new Measure(12, "px"), readBack.minContentMargin.top);
+    assertEquals(new Measure(1, "cm"), readBack.minContentMargin.left);
+    assertNull(readBack.minContentMargin.right);
+  }
+
   /** The C++ suite covers the mode matrix; this only proves the config crosses JNI. */
   @Test
   void viewportModeReachesTheHtml() throws IOException {
diff --git a/python/src/bind_html.cpp b/python/src/bind_html.cpp
index 76c058524..21887c2b5 100644
--- a/python/src/bind_html.cpp
+++ b/python/src/bind_html.cpp
@@ -93,6 +93,7 @@ void odr_python::bind_html(py::module_ &m) {
       .def_readwrite("viewport_content", &odr::HtmlConfig::viewport_content)
       .def_readwrite("viewport_width", &odr::HtmlConfig::viewport_width)
       .def_readwrite("initial_zoom", &odr::HtmlConfig::initial_zoom)
+      .def_readwrite("min_content_margin", &odr::HtmlConfig::min_content_margin)
       .def_readwrite("format_html", &odr::HtmlConfig::format_html)
       .def_readwrite("html_indent", &odr::HtmlConfig::html_indent)
       .def_readwrite("html_indent_string", &odr::HtmlConfig::html_indent_string)
diff --git a/python/tests/test_html.py b/python/tests/test_html.py
index 4f99564c6..475d41db2 100644
--- a/python/tests/test_html.py
+++ b/python/tests/test_html.py
@@ -90,6 +90,29 @@ def render(name, config):
     assert '<meta name="viewport" content="width=420"/>' in render("raw", raw)
 
 
+def test_min_content_margin_reaches_the_html(odt_path, tmp_path):
+    # The C++ suite covers where the floor lands; this only proves it crosses
+    # the binding, unset sides and all.
+    def render(name, config):
+        cache = tmp_path / name
+        cache.mkdir()
+        file = pyodr.open(str(odt_path))
+        service = pyodr.html.translate(file, str(cache), config)
+        content, _ = service.list_views()[0].write_html()
+        return content
+
+    default = pyodr.HtmlConfig()
+    assert default.min_content_margin.top is None
+    assert ":root{--odr-min-margin" not in render("default", default)
+
+    config = pyodr.HtmlConfig()
+    config.min_content_margin.top = pyodr.Measure("12px")
+    config.min_content_margin.left = pyodr.Measure("1cm")
+    html = render("margin", config)
+    assert ":root{--odr-min-margin-top:12px;--odr-min-margin-left:1cm;}" in html
+    assert "--odr-min-margin-right:" not in html
+
+
 def test_translate_text(txt_path, tmp_path):
     html = translate_offline(txt_path, tmp_path)
     pages = html.pages()
diff --git a/src/odr/html.hpp b/src/odr/html.hpp
index fd3f12d3b..96a841b35 100644
--- a/src/odr/html.hpp
+++ b/src/odr/html.hpp
@@ -3,6 +3,7 @@
 #include <odr/document.hpp>
 #include <odr/file.hpp>
 #include <odr/logger.hpp>
+#include <odr/style.hpp>
 #include <odr/table_dimension.hpp>
 
 #include <functional>
@@ -156,6 +157,14 @@ struct HtmlConfig {
   /// The zoom the view opens at, 1 being actual size; unset follows the fit.
   std::optional<double> initial_zoom;
 
+  /// The least distance the generated content keeps from the view's border. A
+  /// side left unset keeps the inset the view already has — `3mm` for a
+  /// reflowed text document, `16px` for the page column and the source views,
+  /// `8px` for a font specimen, none for an image or a file listing. A set
+  /// side raises that inset, never lowers it. A sheet and the media view are
+  /// not inset: the one meets the edge by design, the other is full-bleed.
+  DirectionalStyle<Measure> min_content_margin;
+
   /// Indent and break the output into lines rather than writing one stream.
   bool format_html{false};
   /// Repeated @ref html_indent_string per nesting level; 0 disables indenting.
diff --git a/src/odr/internal/html/common.cpp b/src/odr/internal/html/common.cpp
index 85e9516ce..6ed386929 100644
--- a/src/odr/internal/html/common.cpp
+++ b/src/odr/internal/html/common.cpp
@@ -11,6 +11,8 @@
 #include <odr/style.hpp>
 
 #include <algorithm>
+#include <array>
+#include <cctype>
 #include <cstdint>
 #include <fstream>
 #include <iomanip>
@@ -18,6 +20,7 @@
 #include <string>
 #include <string_view>
 #include <unordered_map>
+#include <utility>
 
 namespace odr::internal {
 
@@ -92,6 +95,70 @@ std::optional<double> html::css_pixels(const std::optional<Measure> &measure) {
   return pixels > 0 ? std::optional(pixels) : std::nullopt;
 }
 
+namespace {
+
+/// Whether @p name is a unit css could read: letters, or a percent sign. Also
+/// what keeps a hosted value from closing the `<style>` element it is written
+/// into.
+bool is_css_unit(const std::string_view name) {
+  if (name.empty()) {
+    return false;
+  }
+  if (name == "%") {
+    return true;
+  }
+  return std::ranges::all_of(name, [](const char c) {
+    return std::isalpha(static_cast<unsigned char>(c)) != 0;
+  });
+}
+
+/// The margin a side states, where css can read it.
+std::optional<Measure> css_margin(const std::optional<Measure> &measure) {
+  if (!measure.has_value() || !is_css_unit(measure->unit().name())) {
+    return {};
+  }
+  return measure;
+}
+
+} // namespace
+
+double html::page_column_gutter_pixels(const HtmlConfig &config) {
+  const auto side = [](const std::optional<Measure> &measure) {
+    return std::max(page_column_side_gutter_pixels,
+                    css_pixels(css_margin(measure)).value_or(0.0));
+  };
+  return side(config.min_content_margin.left) +
+         side(config.min_content_margin.right);
+}
+
+void html::write_content_margin_style(HtmlWriter &out,
+                                      const HtmlConfig &config) {
+  const DirectionalStyle<Measure> &margin = config.min_content_margin;
+
+  const std::array sides{
+      std::pair{std::string_view("top"), css_margin(margin.top)},
+      std::pair{std::string_view("right"), css_margin(margin.right)},
+      std::pair{std::string_view("bottom"), css_margin(margin.bottom)},
+      std::pair{std::string_view("left"), css_margin(margin.left)},
+  };
+
+  if (std::ranges::none_of(
+          sides, [](const auto &side) { return side.second.has_value(); })) {
+    return;
+  }
+
+  out.write_header_style_begin();
+  out.out() << ":root{";
+  for (const auto &[name, measure] : sides) {
+    if (measure.has_value()) {
+      out.out() << "--odr-min-margin-" << name << ":" << measure->to_string()
+                << ";";
+    }
+  }
+  out.out() << "}";
+  out.write_header_style_end();
+}
+
 void html::write_zoom_style(HtmlWriter &out, const HtmlConfig &config,
                             const WidthFit fits,
                             const std::optional<double> content_pixels) {
diff --git a/src/odr/internal/html/common.hpp b/src/odr/internal/html/common.hpp
index 50c401a9b..930658228 100644
--- a/src/odr/internal/html/common.hpp
+++ b/src/odr/internal/html/common.hpp
@@ -61,8 +61,14 @@ width_fit(const HtmlConfig &config, bool fit_width_by_default,
 [[nodiscard]] std::optional<double>
 css_pixels(const std::optional<Measure> &measure);
 
-/// The side gutters the page column puts around its pages, in css pixels.
-constexpr double page_column_gutter_pixels = 32;
+/// One side gutter the page column puts around its pages, in css pixels — what
+/// `.odr-page-outer` and the pdf view's `.p` state as their side margin.
+constexpr double page_column_side_gutter_pixels = 16;
+
+/// Both of them, raised where `config.min_content_margin` asks for more. A side
+/// whose unit does not convert to pixels keeps the built-in gutter: the css
+/// still applies it, only the fit below cannot count it.
+[[nodiscard]] double page_column_gutter_pixels(const HtmlConfig &config);
 
 /// The zoom the view opens at: `--odr-fit` fits @p content_pixels into
 /// `config.viewport_width`, or names who measures it instead, `--odr-zoom` pins
@@ -70,6 +76,11 @@ constexpr double page_column_gutter_pixels = 32;
 void write_zoom_style(HtmlWriter &out, const HtmlConfig &config, WidthFit fits,
                       std::optional<double> content_pixels);
 
+/// `config.min_content_margin` as the `--odr-min-margin-*` the stylesheets
+/// raise their own insets against; nothing at all where no side is set, which
+/// is what keeps the shipped stylesheets independent of the config.
+void write_content_margin_style(HtmlWriter &out, const HtmlConfig &config);
+
 std::string escape_text(std::string text);
 
 /// Escape a string for use as an HTML double-quoted attribute value (`&`, `"`,
diff --git a/src/odr/internal/html/document.cpp b/src/odr/internal/html/document.cpp
index e8a47f68f..fd0939606 100644
--- a/src/odr/internal/html/document.cpp
+++ b/src/odr/internal/html/document.cpp
@@ -33,29 +33,37 @@ bool is_paged_content(const Document &document, const HtmlConfig &config) {
 }
 
 /// A page box plus the gutters the column puts around it, in css pixels.
-std::optional<double> page_content_pixels(const PageLayout &page_layout) {
+std::optional<double> page_content_pixels(const PageLayout &page_layout,
+                                          const HtmlConfig &config) {
   const std::optional<double> width = css_pixels(page_layout.width);
   if (!width.has_value()) {
     return {};
   }
-  return *width + page_column_gutter_pixels;
+  return *width + page_column_gutter_pixels(config);
 }
 
 /// Per view, so slides of differing width are each fitted to their own page.
-std::optional<double> fragment_content_pixels(const TextRoot &element) {
-  return page_content_pixels(element.page_layout());
+std::optional<double> fragment_content_pixels(const TextRoot &element,
+                                              const HtmlConfig &config) {
+  return page_content_pixels(element.page_layout(), config);
 }
-std::optional<double> fragment_content_pixels(const Slide &element) {
-  return page_content_pixels(element.page_layout());
+std::optional<double> fragment_content_pixels(const Slide &element,
+                                              const HtmlConfig &config) {
+  return page_content_pixels(element.page_layout(), config);
 }
-std::optional<double> fragment_content_pixels(const Page &element) {
-  return page_content_pixels(element.page_layout());
+std::optional<double> fragment_content_pixels(const Page &element,
+                                              const HtmlConfig &config) {
+  return page_content_pixels(element.page_layout(), config);
 }
 /// A sheet reflows; there is no page box to fit.
-std::optional<double> fragment_content_pixels(const Sheet &) { return {}; }
+std::optional<double> fragment_content_pixels(const Sheet &,
+                                              const HtmlConfig &) {
+  return {};
+}
 
 /// The widest of them, for the view that writes every page into one file.
-std::optional<double> document_content_pixels(const Document &document) {
+std::optional<double> document_content_pixels(const Document &document,
+                                              const HtmlConfig &config) {
   const Element root = document.root_element();
 
   const auto widest = [](const std::optional<double> lhs,
@@ -69,16 +77,17 @@ std::optional<double> document_content_pixels(const Document &document) {
   std::optional<double> result;
   switch (document.document_type()) {
   case DocumentType::text:
-    result = fragment_content_pixels(root.as_text_root());
+    result = fragment_content_pixels(root.as_text_root(), config);
     break;
   case DocumentType::presentation:
     for (const Element child : root.children()) {
-      result = widest(result, fragment_content_pixels(child.as_slide()));
+      result =
+          widest(result, fragment_content_pixels(child.as_slide(), config));
     }
     break;
   case DocumentType::drawing:
     for (const Element child : root.children()) {
-      result = widest(result, fragment_content_pixels(child.as_page()));
+      result = widest(result, fragment_content_pixels(child.as_page(), config));
     }
     break;
   default:
@@ -121,6 +130,7 @@ void front(const Document &document, const WritingState &state,
                        ? width_fit(state.config(), paged_content, mode_override)
                        : WidthFit::none,
                    content_pixels);
+  write_content_margin_style(out, state.config());
 
   write_document_style(state);
   write_document_dark_style(state);
@@ -193,10 +203,11 @@ class HtmlFragmentBase {
   virtual void write_fragment(HtmlWriter &out, WritingState &state) const = 0;
 
   /// The width this one view lays out, which is what it is fitted against.
-  [[nodiscard]] virtual std::optional<double> content_pixels() const = 0;
+  [[nodiscard]] virtual std::optional<double>
+  content_pixels(const HtmlConfig &config) const = 0;
 
   void write_document(HtmlWriter &out, WritingState &state) const {
-    const std::optional<double> content = content_pixels();
+    const std::optional<double> content = content_pixels(state.config());
     front(m_document, state, m_name, content);
     write_fragment(out, state);
     back(m_document, state);
@@ -346,7 +357,8 @@ class HtmlServiceImpl final : public HtmlService {
     WritingState state(out, config(), resources);
 
     // every page in one file, so the column is as wide as the widest of them
-    const std::optional<double> content = document_content_pixels(m_document);
+    const std::optional<double> content =
+        document_content_pixels(m_document, config());
 
     front(m_document, state, "", content);
     for (const auto &fragment : m_fragments) {
@@ -375,8 +387,10 @@ class TextHtmlFragment final : public HtmlFragmentBase {
       : HtmlFragmentBase(std::move(name), index, std::move(path),
                          std::move(document)) {}
 
-  [[nodiscard]] std::optional<double> content_pixels() const override {
-    return fragment_content_pixels(m_document.root_element().as_text_root());
+  [[nodiscard]] std::optional<double>
+  content_pixels(const HtmlConfig &config) const override {
+    return fragment_content_pixels(m_document.root_element().as_text_root(),
+                                   config);
   }
 
   void write_fragment(HtmlWriter &out, WritingState &state) const override {
@@ -422,8 +436,9 @@ class ElementHtmlFragment final : public HtmlFragmentBase {
                          std::move(document)),
         m_element{element} {}
 
-  [[nodiscard]] std::optional<double> content_pixels() const override {
-    return fragment_content_pixels(m_element);
+  [[nodiscard]] std::optional<double>
+  content_pixels(const HtmlConfig &config) const override {
+    return fragment_content_pixels(m_element, config);
   }
 
   void write_fragment(HtmlWriter &, WritingState &state) const override {
diff --git a/src/odr/internal/html/filesystem.cpp b/src/odr/internal/html/filesystem.cpp
index e1bf97af9..913bef0fd 100644
--- a/src/odr/internal/html/filesystem.cpp
+++ b/src/odr/internal/html/filesystem.cpp
@@ -189,6 +189,7 @@ class HtmlServiceImpl final : public HtmlService {
     out.write_header_title("odr");
     write_viewport_meta(out, config(), false);
     write_zoom_style(out, config(), WidthFit::none, {});
+    write_content_margin_style(out, config());
     write_filesystem_style(state);
     write_filesystem_dark_style(state);
     write_search_style(state);
diff --git a/src/odr/internal/html/font_file.cpp b/src/odr/internal/html/font_file.cpp
index b1555e455..c2f92c68b 100644
--- a/src/odr/internal/html/font_file.cpp
+++ b/src/odr/internal/html/font_file.cpp
@@ -77,6 +77,7 @@ class HtmlServiceImpl final : public HtmlService {
     out.write_header_target("_blank");
     out.write_header_title("odr");
     write_viewport_meta(out, config(), false);
+    write_content_margin_style(out, config());
     out.write_header_end();
 
     out.write_body_begin();
@@ -112,7 +113,10 @@ class HtmlServiceImpl final : public HtmlService {
     out.out() << "@font-face{font-family:'odr-specimen';src:url(" << url
               << ");}";
     // The page's own margin, so it does not depend on the browser's.
-    out.out() << "body{margin:0;padding:8px;background:#fff;"
+    out.out() << "body{margin:0;padding:max(8px,var(--odr-min-margin-top,0px)) "
+                 "max(8px,var(--odr-min-margin-right,0px)) "
+                 "max(8px,var(--odr-min-margin-bottom,0px)) "
+                 "max(8px,var(--odr-min-margin-left,0px));background:#fff;"
                  "font-family:sans-serif;}";
     out.out() << ".grid{display:flex;flex-wrap:wrap;}";
     out.out() << ".cell{width:4em;height:4em;border:1px solid #ddd;margin:2px;"
diff --git a/src/odr/internal/html/frontend.cpp b/src/odr/internal/html/frontend.cpp
index 1f1be61da..913995026 100644
--- a/src/odr/internal/html/frontend.cpp
+++ b/src/odr/internal/html/frontend.cpp
@@ -30,14 +30,15 @@ x-s{display:inline}
    against each other, not against the viewport. The page's side margin is part
    of that width, so fitting the document to a phone screen leaves a gutter
    instead of going edge to edge. */
-.odr-pages{display:flex;flex-direction:column;align-items:center;gap:16px;padding:16px 0;width:max-content;min-width:100%}
+.odr-pages{display:flex;flex-direction:column;align-items:center;gap:16px;padding:max(16px,var(--odr-min-margin-top,0px)) 0 max(16px,var(--odr-min-margin-bottom,0px));width:max-content;min-width:100%}
 /* A stacking context, for the shape backgrounds a page holds at `z-index:-1`.
    Not a negative `z-index`, which is one too but takes the page out of reach of
    hit testing. */
-.odr-page-outer{display:flex;margin:0 16px;background:#fff;box-shadow:0 1px 4px rgba(0,0,0,.5);isolation:isolate}
+.odr-page-outer{display:flex;margin:0 max(16px,var(--odr-min-margin-right,0px)) 0 max(16px,var(--odr-min-margin-left,0px));background:#fff;box-shadow:0 1px 4px rgba(0,0,0,.5);isolation:isolate}
 /* Reflowed to the viewport there is no page box to inset the text. A physical
-   measure, like the page margin it stands in for. */
-.odr-text-flow{padding:3mm}
+   measure, like the page margin it stands in for. `--odr-min-margin-*` is the
+   floor the config puts under it, unset and so inert by default. */
+.odr-text-flow{padding:max(3mm,var(--odr-min-margin-top,0px)) max(3mm,var(--odr-min-margin-right,0px)) max(3mm,var(--odr-min-margin-bottom,0px)) max(3mm,var(--odr-min-margin-left,0px))}
 /* The label is text rather than a `::marker`, which no selection would copy.
    It hangs into the item's padding so wrapped lines align under the text. */
 .odr-list-item{padding-left:2em}
@@ -140,8 +141,8 @@ body{margin:0;background:#fff}
 .odr-text{display:flex;align-items:stretch;min-height:100vh;color:var(--odr-text-fg);font:13px/20px var(--odr-text-mono);tab-size:4}
 /* The numbers are ours, not the file's, so the gutter stays out of a selection
    of the page. */
-.odr-text-nr{display:flex;flex-direction:column;flex:none;padding:16px 12px 16px 16px;text-align:right;color:var(--odr-text-muted);background:var(--odr-text-gutter);border-right:1px solid var(--odr-text-line);font-variant-numeric:tabular-nums;user-select:none;-webkit-user-select:none}
-.odr-text-body{display:flex;flex-direction:column;flex:1;min-width:0;padding:16px;white-space:pre}
+.odr-text-nr{display:flex;flex-direction:column;flex:none;padding:max(16px,var(--odr-min-margin-top,0px)) 12px max(16px,var(--odr-min-margin-bottom,0px)) max(16px,var(--odr-min-margin-left,0px));text-align:right;color:var(--odr-text-muted);background:var(--odr-text-gutter);border-right:1px solid var(--odr-text-line);font-variant-numeric:tabular-nums;user-select:none;-webkit-user-select:none}
+.odr-text-body{display:flex;flex-direction:column;flex:1;min-width:0;padding:max(16px,var(--odr-min-margin-top,0px)) max(16px,var(--odr-min-margin-right,0px)) max(16px,var(--odr-min-margin-bottom,0px)) 16px;white-space:pre}
 .odr-text-wrap{white-space:break-spaces;word-break:break-word;overflow-wrap:anywhere}
 /* A hovered line reaches its number, which is in the other column, by beginning
    a viewport to the left of it; the padding puts the text back where it was.
@@ -178,7 +179,7 @@ constexpr std::string_view xml_css = R"css(
 --odr-xml-mono:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
 }
 body{margin:0;background:#fff}
-.odr-xml{padding:16px;color:var(--odr-xml-text);font:13px/1.6 var(--odr-xml-mono);word-break:break-word;overflow-wrap:anywhere}
+.odr-xml{padding:max(16px,var(--odr-min-margin-top,0px)) max(16px,var(--odr-min-margin-right,0px)) max(16px,var(--odr-min-margin-bottom,0px)) max(16px,var(--odr-min-margin-left,0px));color:var(--odr-xml-text);font:13px/1.6 var(--odr-xml-mono);word-break:break-word;overflow-wrap:anywhere}
 .odr-xml-line,.odr-xml summary{padding-left:1.5em}
 .odr-xml summary{display:block;position:relative;list-style:none;cursor:pointer}
 .odr-xml summary::-webkit-details-marker{display:none}
@@ -222,7 +223,7 @@ constexpr std::string_view filesystem_css = R"css(
 --odr-files-font:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
 --odr-files-mono:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
 }
-body{margin:0;background:#fff;color:#1f2328;font:13px/1.5 var(--odr-files-font)}
+body{margin:0;padding:var(--odr-min-margin-top,0px) var(--odr-min-margin-right,0px) var(--odr-min-margin-bottom,0px) var(--odr-min-margin-left,0px);background:#fff;color:#1f2328;font:13px/1.5 var(--odr-files-font)}
 .odr-files{border-collapse:collapse;width:100%}
 .odr-files td{padding:5px 12px;border-top:1px solid var(--odr-files-line)}
 .odr-files tbody tr:hover>*{background-image:linear-gradient(rgba(0,0,0,.04),rgba(0,0,0,.04))}
diff --git a/src/odr/internal/html/image_file.cpp b/src/odr/internal/html/image_file.cpp
index 7dae30b35..1d558364a 100644
--- a/src/odr/internal/html/image_file.cpp
+++ b/src/odr/internal/html/image_file.cpp
@@ -121,8 +121,13 @@ class HtmlServiceImpl final : public HtmlService {
     // An image has no layout width to preserve, so css alone fits it, framed
     // or not - no measuring and no `viewport_width`.
     write_zoom_style(out, config(), WidthFit::none, {});
+    write_content_margin_style(out, config());
     out.write_header_style_begin();
-    out.out() << "body{margin:0;background:#fff}";
+    // The picture runs to the border unless the config puts a floor under it.
+    out.out() << "body{margin:0;padding:var(--odr-min-margin-top,0px) "
+                 "var(--odr-min-margin-right,0px) "
+                 "var(--odr-min-margin-bottom,0px) "
+                 "var(--odr-min-margin-left,0px);background:#fff}";
     if (width_fit(config(), true) != WidthFit::none) {
       // `100%` of a zoomed body is the viewport again, so the factor has to
       // be put back for the image to grow with it
diff --git a/src/odr/internal/html/pdf_file.cpp b/src/odr/internal/html/pdf_file.cpp
index c646f30ab..e79be122b 100644
--- a/src/odr/internal/html/pdf_file.cpp
+++ b/src/odr/internal/html/pdf_file.cpp
@@ -1718,7 +1718,7 @@ class HtmlServiceImpl final : public HtmlService {
     }
     substitute_faces.append_faces(font_faces);
 
-    const std::optional<double> content = content_pixels(pages_out);
+    const std::optional<double> content = content_pixels(pages_out, config());
     write_header_common(state, font_faces, font_styles, styles, content, [&] {
       // Visual layer glyph spans: not selectable (selection rides the `.sel`
       // layer).
@@ -2194,7 +2194,7 @@ class HtmlServiceImpl final : public HtmlService {
     substitute_faces.append_faces(font_faces);
 
     // ---- Pass 2: write HTML ---------------------------------------------
-    const std::optional<double> content = content_pixels(pages_out);
+    const std::optional<double> content = content_pixels(pages_out, config());
     write_header_common(state, font_faces, font_styles, styles, content, [&] {
       // Invisible text render modes (Tr 3/7).
       out.out() << ".i{color:transparent}";
@@ -2557,8 +2557,8 @@ class HtmlServiceImpl final : public HtmlService {
 
   /// The widest page a view holds, in css pixels, with `.d`'s side gutters.
   template <typename PageOut>
-  static std::optional<double>
-  content_pixels(const std::vector<PageOut> &pages) {
+  static std::optional<double> content_pixels(const std::vector<PageOut> &pages,
+                                              const HtmlConfig &config) {
     double widest = 0;
     for (const PageOut &page : pages) {
       widest = std::max(widest, page.width);
@@ -2566,7 +2566,7 @@ class HtmlServiceImpl final : public HtmlService {
     if (widest <= 0) {
       return {};
     }
-    return widest * pt_to_in * 96.0 + page_column_gutter_pixels;
+    return widest * pt_to_in * 96.0 + page_column_gutter_pixels(config);
   }
 
   /// The document/head prologue shared by both modes, with `write_mode_css()`
@@ -2587,16 +2587,21 @@ class HtmlServiceImpl final : public HtmlService {
     out.write_header_title("odr");
     write_viewport_meta(out, config(), true);
     write_zoom_style(out, config(), width_fit(config(), true), content);
+    write_content_margin_style(out, config());
     out.write_header_style_begin();
     out.out() << "body{margin:0;background:#525659}";
     // `.d`: the page column, sized to the widest page so pages of differing
     // width centre against each other rather than against the viewport. Their
     // side margin is part of that width, so a phone screen keeps a gutter.
     out.out() << ".d{display:flex;flex-direction:column;align-items:center;"
-                 "gap:16px;padding:16px 0;width:max-content;min-width:100%}";
+                 "gap:16px;padding:max(16px,var(--odr-min-margin-top,0px)) 0 "
+                 "max(16px,var(--odr-min-margin-bottom,0px));"
+                 "width:max-content;min-width:100%}";
     // `overflow:hidden` clips to the crop box, as a viewer does: content may
     // sit outside it (a bleed, or an InDesign spread's other page).
-    out.out() << ".p{position:relative;margin:0 16px;background:#fff;"
+    out.out() << ".p{position:relative;"
+                 "margin:0 max(16px,var(--odr-min-margin-right,0px)) 0 "
+                 "max(16px,var(--odr-min-margin-left,0px));background:#fff;"
                  "overflow:hidden;box-shadow:0 1px 4px rgba(0,0,0,.5)}";
     // `.t`: shared base for all absolutely-positioned line blocks.
     // `font-size:0` collapses its strut, which outranks the run it holds and
diff --git a/src/odr/internal/html/text_file.cpp b/src/odr/internal/html/text_file.cpp
index 4016ec7d9..38df832c8 100644
--- a/src/odr/internal/html/text_file.cpp
+++ b/src/odr/internal/html/text_file.cpp
@@ -100,6 +100,7 @@ class HtmlServiceImpl final : public HtmlService {
     out.write_header_title("odr");
     write_viewport_meta(out, config(), false);
     write_zoom_style(out, config(), WidthFit::none, {});
+    write_content_margin_style(out, config());
 
     write_text_style(state);
     write_text_dark_style(state);
diff --git a/src/odr/internal/html/xml_file.cpp b/src/odr/internal/html/xml_file.cpp
index 14064f39f..bcd52cb1d 100644
--- a/src/odr/internal/html/xml_file.cpp
+++ b/src/odr/internal/html/xml_file.cpp
@@ -260,6 +260,7 @@ class HtmlServiceImpl final : public HtmlService {
     out.write_header_title("odr");
     write_viewport_meta(out, config(), false);
     write_zoom_style(out, config(), WidthFit::none, {});
+    write_content_margin_style(out, config());
 
     write_xml_style(state);
     write_xml_dark_style(state);
diff --git a/test/data.cmake b/test/data.cmake
index 9bcaea825..5742c25d7 100644
--- a/test/data.cmake
+++ b/test/data.cmake
@@ -17,9 +17,9 @@ odr_test_data(
 odr_test_data(
         PATH "reference-output/odr-public"
         URL "https://github.com/opendocument-app/OpenDocument.test.output.git"
-        REVISION "f211f7544b400cb69b13e277a6c280e131a05c65")
+        REVISION "280cafc1747882ea600cb5ff96a68ced3af81712")
 
 odr_test_data(
         PATH "reference-output/odr-private"
         URL "https://github.com/opendocument-app/OpenDocument.test-private.output.git"
-        REVISION "eacdb50e9cd6791538708c6be6b288e077cc4a0b")
+        REVISION "e813a20df7b0623768e8eb2afb83b80f83d43f42")
diff --git a/test/src/html_test.cpp b/test/src/html_test.cpp
index 3b3365b54..a8ac2f1ee 100644
--- a/test/src/html_test.cpp
+++ b/test/src/html_test.cpp
@@ -1,7 +1,9 @@
 #include <algorithm>
 #include <filesystem>
 #include <fstream>
+#include <optional>
 #include <sstream>
+#include <string>
 #include <tuple>
 
 #include <odr/html.hpp>
@@ -220,6 +222,76 @@ TEST(html, flowing_text_is_inset_from_the_screen_edge) {
   EXPECT_NE(page.find(".odr-text-flow{padding:"), std::string::npos);
 }
 
+// Unset it writes nothing at all, which is what keeps the shipped stylesheets
+// independent of the config.
+TEST(html, min_content_margin_is_written_only_where_it_is_set) {
+  HtmlConfig config;
+  config.text_document_margin = false;
+
+  // the stylesheets name the variables either way; nobody declares one
+  EXPECT_EQ(render_odt(config).find(":root{--odr-min-margin"),
+            std::string::npos);
+
+  config.min_content_margin.top = Measure("12px");
+  config.min_content_margin.left = Measure("1cm");
+  const std::string page = render_odt(config);
+
+  EXPECT_NE(page.find(":root{--odr-min-margin-top:12px;--odr-min-margin-left:"
+                      "1cm;}"),
+            std::string::npos);
+  EXPECT_EQ(page.find("--odr-min-margin-right:"), std::string::npos);
+}
+
+// The value reaches the page a host would host, so a unit css cannot read is
+// dropped rather than written into the style element.
+TEST(html, min_content_margin_drops_a_unit_css_cannot_read) {
+  HtmlConfig config;
+  config.min_content_margin.top =
+      Measure("1px;}</style><script>alert(1)</script>");
+
+  const std::string page = render_odt(config);
+
+  EXPECT_EQ(page.find(":root{--odr-min-margin"), std::string::npos);
+  EXPECT_EQ(page.find("<script>alert"), std::string::npos);
+}
+
+namespace {
+
+/// The `--odr-fit` @p page states, or nothing where it follows its own size.
+std::optional<double> fit_of(const std::string &page) {
+  const std::size_t begin = page.find("--odr-fit:");
+  if (begin == std::string::npos) {
+    return {};
+  }
+  return std::stod(page.substr(begin + std::string("--odr-fit:").length()));
+}
+
+} // namespace
+
+// The gutter around the page column is part of the width the view is fitted
+// to, so raising it fits the pages smaller.
+TEST(html, min_content_margin_widens_the_page_column_fit) {
+  HtmlConfig config;
+  config.text_document_margin = true;
+  config.viewport_width = 400;
+
+  const std::optional<double> narrow = fit_of(render_odt(config));
+  ASSERT_TRUE(narrow.has_value());
+
+  config.min_content_margin.left = Measure("100px");
+  config.min_content_margin.right = Measure("100px");
+  const std::optional<double> wide = fit_of(render_odt(config));
+  ASSERT_TRUE(wide.has_value());
+
+  EXPECT_LT(*wide, *narrow);
+
+  // A unit the fit cannot convert leaves it where it was; the css still
+  // applies the margin.
+  config.min_content_margin.left = Measure("100em");
+  config.min_content_margin.right = Measure("100em");
+  EXPECT_EQ(fit_of(render_odt(config)), narrow);
+}
+
 // For `system` it is the element carrying the dark style that is gated, not a
 // rule inside it.
 TEST(html, color_scheme_writes_the_dark_style) {
diff --git a/wasm/js/index.d.ts b/wasm/js/index.d.ts
index 8fe9cf376..6ce29ecf4 100644
--- a/wasm/js/index.d.ts
+++ b/wasm/js/index.d.ts
@@ -91,6 +91,17 @@ export interface HtmlConfig {
   viewportWidth?: number;
   /** The zoom the view opens at, 1 being actual size; unset follows the fit. */
   initialZoom?: number;
+  /**
+   * The least distance the generated content keeps from the view's border, per
+   * side, as a css length (e.g. `"3mm"`). An omitted side keeps the inset the
+   * view already has; a given side raises it, never lowers it.
+   */
+  minContentMargin?: {
+    top?: string;
+    right?: string;
+    bottom?: string;
+    left?: string;
+  };
   pdfTextMode?: number;
 }
 
diff --git a/wasm/src/wasm_html.cpp b/wasm/src/wasm_html.cpp
index f63b4565e..26c885d4f 100644
--- a/wasm/src/wasm_html.cpp
+++ b/wasm/src/wasm_html.cpp
@@ -6,6 +6,7 @@
 
 #include <emscripten/bind.h>
 
+#include <optional>
 #include <sstream>
 #include <string>
 
@@ -34,6 +35,16 @@ void read_enum(const emscripten::val &value, const char *key, T &target) {
   target = static_cast<T>(field.as<int>());
 }
 
+/// A css length a caller states as a string, e.g. `"3mm"`.
+void read_measure(const emscripten::val &value, const char *key,
+                  std::optional<Measure> &target) {
+  const emscripten::val field = value[key];
+  if (field.isUndefined() || field.isNull()) {
+    return;
+  }
+  target = Measure(field.as<std::string>());
+}
+
 /// Translates on first use, so a caller that only wants metadata does not pay
 /// for a render at open.
 Session &warm(const Handle handle) {
@@ -151,6 +162,14 @@ HtmlConfig to_html_config(const emscripten::val &value) {
   }
   read_enum(value, "pdfTextMode", config.pdf_text_mode);
 
+  if (const emscripten::val margin = value["minContentMargin"];
+      !margin.isUndefined() && !margin.isNull()) {
+    read_measure(margin, "top", config.min_content_margin.top);
+    read_measure(margin, "right", config.min_content_margin.right);
+    read_measure(margin, "bottom", config.min_content_margin.bottom);
+    read_measure(margin, "left", config.min_content_margin.left);
+  }
+
   return config;
 }
 
diff --git a/wasm/tests/render.test.mjs b/wasm/tests/render.test.mjs
index 51b66ddf3..978ab2031 100644
--- a/wasm/tests/render.test.mjs
+++ b/wasm/tests/render.test.mjs
@@ -76,6 +76,26 @@ describe('render', () => {
     }
   });
 
+  // The C++ suite covers where the floor lands; this only proves the sides
+  // cross the binding as css lengths, omitted ones staying omitted.
+  it('honours a minimum content margin', () => {
+    const plain = odr.open(fixture('mixed-layout.odt'));
+    const inset = odr.open(fixture('mixed-layout.odt'), {
+      minContentMargin: { top: '12px', left: '1cm' },
+    });
+    try {
+      assert.ok(!plain.render(0).html.includes(':root{--odr-min-margin'));
+      const html = inset.render(0).html;
+      assert.ok(
+        html.includes(':root{--odr-min-margin-top:12px;--odr-min-margin-left:1cm;}'),
+      );
+      assert.ok(!html.includes('--odr-min-margin-right:'));
+    } finally {
+      plain.close();
+      inset.close();
+    }
+  });
+
   it('honours a config passed at open', () => {
     const plain = odr.open(fixture('mixed-layout.odt'));
     const editable = odr.open(fixture('mixed-layout.odt'), { editable: true });

From cecc36dfedd6f75f6d78f0feafa9ed122e04c4b4 Mon Sep 17 00:00:00 2001
From: Andreas Stefl <stefl.andreas@gmail.com>
Date: Thu, 27 Aug 2026 08:05:15 +0200
Subject: [PATCH 2/2] fix(html): take a content margin only where css reads it
 as a length

`is_css_unit` accepted any alphabetic unit, so a value css cannot resolve
was written into `--odr-min-margin-*` and voided the whole shorthand that
floors an inset against it - the opposite of raising it - while the fit
kept counting a gutter the page no longer had.

One predicate now decides both paths: a finite, positive magnitude with a
css length unit, matched case-insensitively. Everything else keeps the
built-in inset. `css_pixels` folds case and drops a non-finite result too,
which makes it a subset again, so the fit calls it directly.

Cover it a level down, in `html_common`, and render every view that writes
the declaration rather than only the odt document view.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GzAvJtjXwfvy7c5yMxsJpu
---
 CHANGELOG.md                                  |  9 +-
 apple/include/OdrCoreObjC/ODRHtml.h           |  3 +-
 apple/include/OdrCoreObjC/ODRStyle.h          |  3 +-
 .../app/opendocument/core/HtmlConfig.java     |  4 +-
 jni/tests/app/opendocument/core/HtmlTest.java |  5 ++
 src/odr/html.hpp                              |  7 +-
 src/odr/internal/html/common.cpp              | 87 +++++++++++--------
 src/odr/internal/html/common.hpp              | 14 ++-
 src/odr/internal/html/frontend.cpp            |  4 +-
 test/src/html_test.cpp                        | 83 +++++++++++-------
 test/src/internal/html/common_test.cpp        | 83 ++++++++++++++++++
 wasm/js/index.d.ts                            |  4 +-
 12 files changed, 213 insertions(+), 93 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4eeedd26c..636f818a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,12 +17,9 @@ The release run heads these entries with the version and opens a fresh
 ## Unreleased
 
 - `HtmlConfig::min_content_margin` puts a floor under the distance the
-  generated content keeps from the view's border, per side. Unset, every view
-  keeps the inset it has today; a set side raises it - in a reflowed text
-  document, the page column of a text, presentation, drawing or pdf view, the
-  text and xml source views, the file listing, the image view and the font
-  specimen. A sheet and the media view are not inset. Bound in python, jni,
-  wasm (`minContentMargin`, css lengths as strings) and apple.
+  generated content keeps from the view's border, per side. A set side raises
+  the inset a view already has, never lowers it; a sheet is never inset. Bound
+  in python, jni, wasm and apple as `minContentMargin`.
 - **Breaking** Bytes that do not read as text no longer come back as
   `text_file` and render as nonsense - `decode` throws `UnknownFileType` and
   `list_file_types` comes back empty. A file is text when it is empty, or its
diff --git a/apple/include/OdrCoreObjC/ODRHtml.h b/apple/include/OdrCoreObjC/ODRHtml.h
index ab6227ba5..33899c11a 100644
--- a/apple/include/OdrCoreObjC/ODRHtml.h
+++ b/apple/include/OdrCoreObjC/ODRHtml.h
@@ -103,8 +103,7 @@ NS_SWIFT_NAME(HtmlConfig)
 @property(nonatomic, strong, nullable) NSNumber *initialZoom;
 
 /// The least distance the generated content keeps from the view's border. A
-/// `nil` side keeps the inset the view already has; a set side raises it,
-/// never lowers it.
+/// set side raises the inset the view already has, never lowers it.
 @property(nonatomic, strong) ODRDirectionalMeasure *minContentMargin;
 
 @property(nonatomic) BOOL formatHtml;
diff --git a/apple/include/OdrCoreObjC/ODRStyle.h b/apple/include/OdrCoreObjC/ODRStyle.h
index 668b75d0e..a0c0dc760 100644
--- a/apple/include/OdrCoreObjC/ODRStyle.h
+++ b/apple/include/OdrCoreObjC/ODRStyle.h
@@ -97,8 +97,7 @@ NS_SWIFT_NAME(DirectionalMeasure)
 @property(nonatomic, readonly, nullable) ODRMeasure *left;
 @property(nonatomic, readonly, nullable) ODRMeasure *bottom;
 
-/// For the sides a caller states itself, e.g.
-/// @ref ODRHtmlConfig.minContentMargin.
+/// For the sides a caller states itself, e.g. `ODRHtmlConfig.minContentMargin`.
 - (instancetype)initWithRight:(nullable ODRMeasure *)right
                           top:(nullable ODRMeasure *)top
                          left:(nullable ODRMeasure *)left
diff --git a/jni/java/app/opendocument/core/HtmlConfig.java b/jni/java/app/opendocument/core/HtmlConfig.java
index 699ab8ce3..651cb96c2 100644
--- a/jni/java/app/opendocument/core/HtmlConfig.java
+++ b/jni/java/app/opendocument/core/HtmlConfig.java
@@ -43,8 +43,8 @@ public final class HtmlConfig {
   public Double initialZoom;
 
   /**
-   * The least distance the generated content keeps from the view's border. A {@code null} side
-   * keeps the inset the view already has; a set side raises it, never lowers it.
+   * The least distance the generated content keeps from the view's border. A set side raises the
+   * inset the view already has, never lowers it.
    */
   public DirectionalMeasure minContentMargin =
       new DirectionalMeasure(null, null, null, null);
diff --git a/jni/tests/app/opendocument/core/HtmlTest.java b/jni/tests/app/opendocument/core/HtmlTest.java
index fd33ff5ae..a18e85621 100644
--- a/jni/tests/app/opendocument/core/HtmlTest.java
+++ b/jni/tests/app/opendocument/core/HtmlTest.java
@@ -68,6 +68,11 @@ void minContentMarginReachesTheHtml() throws IOException {
     assertNull(new HtmlConfig().minContentMargin.top);
     assertTrue(!renderOdt(new HtmlConfig()).contains(":root{--odr-min-margin"));
 
+    // the field is the host's to null, and reading one is not a crash
+    HtmlConfig cleared = new HtmlConfig();
+    cleared.minContentMargin = null;
+    assertTrue(!renderOdt(cleared).contains(":root{--odr-min-margin"));
+
     HtmlConfig config = new HtmlConfig();
     config.minContentMargin =
         new DirectionalMeasure(null, new Measure(12, "px"), new Measure(1, "cm"), null);
diff --git a/src/odr/html.hpp b/src/odr/html.hpp
index 96a841b35..445be5a93 100644
--- a/src/odr/html.hpp
+++ b/src/odr/html.hpp
@@ -158,11 +158,8 @@ struct HtmlConfig {
   std::optional<double> initial_zoom;
 
   /// The least distance the generated content keeps from the view's border. A
-  /// side left unset keeps the inset the view already has — `3mm` for a
-  /// reflowed text document, `16px` for the page column and the source views,
-  /// `8px` for a font specimen, none for an image or a file listing. A set
-  /// side raises that inset, never lowers it. A sheet and the media view are
-  /// not inset: the one meets the edge by design, the other is full-bleed.
+  /// set side raises the inset the view already has, never lowers it; a unit
+  /// css cannot read as a length is ignored. A sheet is never inset.
   DirectionalStyle<Measure> min_content_margin;
 
   /// Indent and break the output into lines rather than writing one stream.
diff --git a/src/odr/internal/html/common.cpp b/src/odr/internal/html/common.cpp
index 6ed386929..56f5503e4 100644
--- a/src/odr/internal/html/common.cpp
+++ b/src/odr/internal/html/common.cpp
@@ -12,7 +12,7 @@
 
 #include <algorithm>
 #include <array>
-#include <cctype>
+#include <cmath>
 #include <cstdint>
 #include <fstream>
 #include <iomanip>
@@ -20,6 +20,7 @@
 #include <string>
 #include <string_view>
 #include <unordered_map>
+#include <unordered_set>
 #include <utility>
 
 namespace odr::internal {
@@ -76,56 +77,74 @@ html::width_fit(const HtmlConfig &config, const bool fit_width_by_default,
   }
 }
 
-std::optional<double> html::css_pixels(const std::optional<Measure> &measure) {
-  if (!measure.has_value()) {
-    return {};
-  }
+namespace {
 
-  // css absolute lengths, all defined against the inch (css values 3, 5.2).
-  static const std::unordered_map<std::string, double> per_unit{
-      {"px", 1.0},      {"in", 96.0},        {"pt", 96.0 / 72.0},
-      {"pc", 96.0 / 6}, {"cm", 96.0 / 2.54}, {"mm", 96.0 / 25.4},
+/// css absolute lengths, all defined against the inch (css values 3, 5.2).
+const std::unordered_map<std::string, double> &css_absolute_units() {
+  static const std::unordered_map<std::string, double> units{
+      {"px", 1.0},         {"in", 96.0},        {"pt", 96.0 / 72.0},
+      {"pc", 96.0 / 6},    {"cm", 96.0 / 2.54}, {"mm", 96.0 / 25.4},
+      {"q", 96.0 / 101.6},
   };
-
-  const auto it = per_unit.find(std::string(measure->unit().name()));
-  if (it == std::end(per_unit)) {
-    return {};
-  }
-  const double pixels = measure->magnitude() * it->second;
-  return pixels > 0 ? std::optional(pixels) : std::nullopt;
+  return units;
 }
 
-namespace {
+/// Whether css reads @p name as a length: an absolute one, one it resolves
+/// against the font, the line or the viewport, or `%` against the containing
+/// block.
+bool is_css_length_unit(const std::string &name) {
+  static const std::unordered_set<std::string> relative{
+      "em", "rem", "ex", "ch", "ic",   "cap",  "lh", "rlh",
+      "vw", "vh",  "vi", "vb", "vmin", "vmax", "%",
+  };
+  return css_absolute_units().contains(name) || relative.contains(name);
+}
 
-/// Whether @p name is a unit css could read: letters, or a percent sign. Also
-/// what keeps a hosted value from closing the `<style>` element it is written
-/// into.
-bool is_css_unit(const std::string_view name) {
-  if (name.empty()) {
-    return false;
-  }
-  if (name == "%") {
-    return true;
-  }
-  return std::ranges::all_of(name, [](const char c) {
-    return std::isalpha(static_cast<unsigned char>(c)) != 0;
-  });
+/// Unit identifiers are case-insensitive in css, and a host writes the name.
+std::string unit_name(const Measure &measure) {
+  return util::string::to_lower(measure.unit().name());
 }
 
-/// The margin a side states, where css can read it.
+/// One side gutter the page column puts around its pages, in css pixels — what
+/// `.odr-page-outer` and the pdf view's `.p` state as their side margin.
+constexpr double page_column_side_gutter_pixels = 16;
+
+/// The margin a side states, where css can read it as a length. Anything else
+/// keeps the built-in inset: every rule floors its own against a `max()`, and a
+/// `var()` css cannot resolve voids the whole shorthand rather than the side.
 std::optional<Measure> css_margin(const std::optional<Measure> &measure) {
-  if (!measure.has_value() || !is_css_unit(measure->unit().name())) {
+  if (!measure.has_value()) {
+    return {};
+  }
+  const double magnitude = measure->magnitude();
+  if (!std::isfinite(magnitude) || magnitude <= 0) {
     return {};
   }
-  return measure;
+  return is_css_length_unit(unit_name(*measure)) ? measure : std::nullopt;
 }
 
 } // namespace
 
+std::optional<double> html::css_pixels(const std::optional<Measure> &measure) {
+  if (!measure.has_value()) {
+    return {};
+  }
+
+  const auto &units = css_absolute_units();
+  const auto it = units.find(unit_name(*measure));
+  if (it == std::end(units)) {
+    return {};
+  }
+  const double pixels = measure->magnitude() * it->second;
+  return std::isfinite(pixels) && pixels > 0 ? std::optional(pixels)
+                                             : std::nullopt;
+}
+
 double html::page_column_gutter_pixels(const HtmlConfig &config) {
+  // Whatever `css_margin` drops, `css_pixels` drops too, so it need not run.
   const auto side = [](const std::optional<Measure> &measure) {
     return std::max(page_column_side_gutter_pixels,
-                    css_pixels(css_margin(measure)).value_or(0.0));
+                    css_pixels(measure).value_or(0.0));
   };
   return side(config.min_content_margin.left) +
          side(config.min_content_margin.right);
diff --git a/src/odr/internal/html/common.hpp b/src/odr/internal/html/common.hpp
index 930658228..6eab71fe5 100644
--- a/src/odr/internal/html/common.hpp
+++ b/src/odr/internal/html/common.hpp
@@ -61,13 +61,9 @@ width_fit(const HtmlConfig &config, bool fit_width_by_default,
 [[nodiscard]] std::optional<double>
 css_pixels(const std::optional<Measure> &measure);
 
-/// One side gutter the page column puts around its pages, in css pixels — what
-/// `.odr-page-outer` and the pdf view's `.p` state as their side margin.
-constexpr double page_column_side_gutter_pixels = 16;
-
-/// Both of them, raised where `config.min_content_margin` asks for more. A side
-/// whose unit does not convert to pixels keeps the built-in gutter: the css
-/// still applies it, only the fit below cannot count it.
+/// Both side gutters the page column puts around its pages, in css pixels,
+/// raised where `config.min_content_margin` asks for more. A side the css
+/// resolves but this cannot — `em`, `%` — keeps the built-in gutter here.
 [[nodiscard]] double page_column_gutter_pixels(const HtmlConfig &config);
 
 /// The zoom the view opens at: `--odr-fit` fits @p content_pixels into
@@ -77,8 +73,8 @@ void write_zoom_style(HtmlWriter &out, const HtmlConfig &config, WidthFit fits,
                       std::optional<double> content_pixels);
 
 /// `config.min_content_margin` as the `--odr-min-margin-*` the stylesheets
-/// raise their own insets against; nothing at all where no side is set, which
-/// is what keeps the shipped stylesheets independent of the config.
+/// floor their insets against; nothing at all where no side states a css
+/// length, which leaves those insets as shipped.
 void write_content_margin_style(HtmlWriter &out, const HtmlConfig &config);
 
 std::string escape_text(std::string text);
diff --git a/src/odr/internal/html/frontend.cpp b/src/odr/internal/html/frontend.cpp
index 913995026..1f328f16d 100644
--- a/src/odr/internal/html/frontend.cpp
+++ b/src/odr/internal/html/frontend.cpp
@@ -36,8 +36,8 @@ x-s{display:inline}
    hit testing. */
 .odr-page-outer{display:flex;margin:0 max(16px,var(--odr-min-margin-right,0px)) 0 max(16px,var(--odr-min-margin-left,0px));background:#fff;box-shadow:0 1px 4px rgba(0,0,0,.5);isolation:isolate}
 /* Reflowed to the viewport there is no page box to inset the text. A physical
-   measure, like the page margin it stands in for. `--odr-min-margin-*` is the
-   floor the config puts under it, unset and so inert by default. */
+   measure, like the page margin it stands in for; `--odr-min-margin-*` is the
+   floor the config puts under it, and is unset by default. */
 .odr-text-flow{padding:max(3mm,var(--odr-min-margin-top,0px)) max(3mm,var(--odr-min-margin-right,0px)) max(3mm,var(--odr-min-margin-bottom,0px)) max(3mm,var(--odr-min-margin-left,0px))}
 /* The label is text rather than a `::marker`, which no selection would copy.
    It hangs into the item's padding so wrapped lines align under the text. */
diff --git a/test/src/html_test.cpp b/test/src/html_test.cpp
index a8ac2f1ee..2f936b372 100644
--- a/test/src/html_test.cpp
+++ b/test/src/html_test.cpp
@@ -1,9 +1,12 @@
 #include <algorithm>
+#include <array>
+#include <cctype>
 #include <filesystem>
 #include <fstream>
 #include <optional>
 #include <sstream>
 #include <string>
+#include <string_view>
 #include <tuple>
 
 #include <odr/html.hpp>
@@ -222,48 +225,70 @@ TEST(html, flowing_text_is_inset_from_the_screen_edge) {
   EXPECT_NE(page.find(".odr-text-flow{padding:"), std::string::npos);
 }
 
-// Unset it writes nothing at all, which is what keeps the shipped stylesheets
-// independent of the config.
-TEST(html, min_content_margin_is_written_only_where_it_is_set) {
+// Every view that insets its content declares the floor it was given; unset it
+// declares nothing, which leaves the shipped stylesheets alone.
+TEST(html, min_content_margin_reaches_every_view) {
   HtmlConfig config;
-  config.text_document_margin = false;
-
-  // the stylesheets name the variables either way; nobody declares one
-  EXPECT_EQ(render_odt(config).find(":root{--odr-min-margin"),
-            std::string::npos);
 
-  config.min_content_margin.top = Measure("12px");
-  config.min_content_margin.left = Measure("1cm");
-  const std::string page = render_odt(config);
+  const auto render_as = [&](const std::string &path, const FileType as) {
+    const DecodedFile file(TestData::test_file_path(path), as, Logger::null());
+    std::ostringstream out;
+    html::translate(file, config).list_views().at(0).write_html(out);
+    return std::move(out).str();
+  };
 
-  EXPECT_NE(page.find(":root{--odr-min-margin-top:12px;--odr-min-margin-left:"
-                      "1cm;}"),
-            std::string::npos);
-  EXPECT_EQ(page.find("--odr-min-margin-right:"), std::string::npos);
-}
+  const auto xml = [&] {
+    const DecodedFile file(File::from_memory("<a><b>c</b></a>"), FileType::xml);
+    std::ostringstream out;
+    html::translate(file, config).list_views().at(0).write_html(out);
+    return std::move(out).str();
+  };
 
-// The value reaches the page a host would host, so a unit css cannot read is
-// dropped rather than written into the style element.
-TEST(html, min_content_margin_drops_a_unit_css_cannot_read) {
-  HtmlConfig config;
-  config.min_content_margin.top =
-      Measure("1px;}</style><script>alert(1)</script>");
+  const auto every_view = [&] {
+    return std::array{
+        // a document, and the page column it stacks
+        render_odt(config),
+        render("odr-public/txt/lorem ipsum.txt", config),
+        xml(),
+        // a file listing: the archive view of a zip
+        render_as("odr-public/odt/about.odt", FileType::zip),
+        render_as("odr-public/png/tango-example-icons.png",
+                  FileType::portable_network_graphics),
+        render_as("odr-public/pdf/empty.pdf",
+                  FileType::portable_document_format),
+        render_as("odr-private/otf/OpenSans-Regular.otf",
+                  FileType::opentype_font),
+    };
+  };
 
-  const std::string page = render_odt(config);
+  for (const std::string &page : every_view()) {
+    EXPECT_EQ(page.find("--odr-min-margin-left:"), std::string::npos);
+  }
 
-  EXPECT_EQ(page.find(":root{--odr-min-margin"), std::string::npos);
-  EXPECT_EQ(page.find("<script>alert"), std::string::npos);
+  config.min_content_margin.left = Measure("7px");
+  for (const std::string &page : every_view()) {
+    EXPECT_NE(page.find(":root{--odr-min-margin-left:7px;}"),
+              std::string::npos);
+  }
 }
 
 namespace {
 
-/// The `--odr-fit` @p page states, or nothing where it follows its own size.
+/// The `--odr-fit` @p page states as a factor, or nothing where it names who
+/// measures it instead.
 std::optional<double> fit_of(const std::string &page) {
-  const std::size_t begin = page.find("--odr-fit:");
-  if (begin == std::string::npos) {
+  constexpr std::string_view key = "--odr-fit:";
+  const std::size_t at = page.find(key);
+  if (at == std::string::npos) {
+    return {};
+  }
+  // `auto` and `view` name a measurer rather than stating a factor
+  const std::size_t begin = at + key.length();
+  if (begin >= page.length() ||
+      std::isdigit(static_cast<unsigned char>(page[begin])) == 0) {
     return {};
   }
-  return std::stod(page.substr(begin + std::string("--odr-fit:").length()));
+  return std::stod(page.substr(begin));
 }
 
 } // namespace
diff --git a/test/src/internal/html/common_test.cpp b/test/src/internal/html/common_test.cpp
index 5975eda2f..ca128728a 100644
--- a/test/src/internal/html/common_test.cpp
+++ b/test/src/internal/html/common_test.cpp
@@ -6,8 +6,10 @@
 
 #include <gtest/gtest.h>
 
+#include <limits>
 #include <optional>
 #include <sstream>
+#include <string>
 
 using namespace odr;
 namespace ihtml = odr::internal::html;
@@ -217,6 +219,87 @@ TEST(html_common, a_zoom_pinned_to_actual_size_is_still_a_pin) {
             styled(":root{--odr-fit:0.5;--odr-zoom:0.5}body{zoom:0.5}"));
 }
 
+namespace {
+
+std::string emit_margin(const HtmlConfig &config) {
+  std::ostringstream out;
+  ihtml::HtmlWriter writer(out, false, "");
+  ihtml::write_content_margin_style(writer, config);
+  return out.str();
+}
+
+} // namespace
+
+TEST(html_common, the_content_margin_states_the_sides_that_are_set) {
+  HtmlConfig config;
+
+  // unset it declares nothing, which leaves the shipped insets as they are
+  EXPECT_EQ(emit_margin(config), "");
+
+  config.min_content_margin.top = Measure("12px");
+  config.min_content_margin.left = Measure("1cm");
+  EXPECT_EQ(emit_margin(config), "<style>:root{--odr-min-margin-top:12px;"
+                                 "--odr-min-margin-left:1cm;}</style>");
+}
+
+// The stylesheets floor their insets with `max(16px,var(--odr-min-margin-*))`,
+// so a value css cannot resolve voids the whole shorthand rather than one side
+// — it has to be dropped here instead.
+TEST(html_common, the_content_margin_drops_what_css_cannot_read_as_a_length) {
+  HtmlConfig config;
+
+  const auto emit = [&](const Measure &measure) {
+    config.min_content_margin = {};
+    config.min_content_margin.top = measure;
+    return emit_margin(config);
+  };
+
+  // a unit that is neither a css length nor closes the style element
+  EXPECT_EQ(emit(Measure("1foo")), "");
+  EXPECT_EQ(emit(Measure("1px;}</style><script>alert(1)</script>")), "");
+  EXPECT_EQ(emit(Measure(1, DynamicUnit())), "");
+
+  // a magnitude that renders no length
+  EXPECT_EQ(emit(Measure(-1, DynamicUnit("px"))), "");
+  EXPECT_EQ(emit(Measure(0, DynamicUnit("px"))), "");
+  EXPECT_EQ(
+      emit(Measure(std::numeric_limits<double>::infinity(), DynamicUnit("px"))),
+      "");
+  EXPECT_EQ(emit(Measure(std::numeric_limits<double>::quiet_NaN(),
+                         DynamicUnit("px"))),
+            "");
+
+  // what css does read is written verbatim, unit case and all
+  EXPECT_NE(emit(Measure("2EM")).find("--odr-min-margin-top:2EM;"),
+            std::string::npos);
+  EXPECT_NE(emit(Measure("50%")).find("--odr-min-margin-top:50%;"),
+            std::string::npos);
+}
+
+TEST(html_common, the_page_column_gutter_is_raised_but_never_lowered) {
+  HtmlConfig config;
+
+  // the 16px per side the stylesheets state
+  EXPECT_EQ(ihtml::page_column_gutter_pixels(config), 32);
+
+  config.min_content_margin.left = Measure("100px");
+  EXPECT_EQ(ihtml::page_column_gutter_pixels(config), 116);
+
+  config.min_content_margin.right = Measure("100PX");
+  EXPECT_EQ(ihtml::page_column_gutter_pixels(config), 200);
+
+  // a smaller floor changes nothing, and the top and bottom are no gutter
+  config.min_content_margin.left = Measure("1px");
+  config.min_content_margin.right = Measure("1px");
+  config.min_content_margin.top = Measure("100px");
+  EXPECT_EQ(ihtml::page_column_gutter_pixels(config), 32);
+
+  // css applies these, the fit cannot count them
+  config.min_content_margin.left = Measure("100em");
+  config.min_content_margin.right = Measure("50%");
+  EXPECT_EQ(ihtml::page_column_gutter_pixels(config), 32);
+}
+
 TEST(html_common, an_opaque_color_is_a_hex_triplet) {
   EXPECT_EQ(ihtml::color(Color(1, 2, 3)), "#010203");
   EXPECT_EQ(ihtml::color(Color(1, 2, 3, 255)), "#010203");
diff --git a/wasm/js/index.d.ts b/wasm/js/index.d.ts
index 6ce29ecf4..db6a20833 100644
--- a/wasm/js/index.d.ts
+++ b/wasm/js/index.d.ts
@@ -93,8 +93,8 @@ export interface HtmlConfig {
   initialZoom?: number;
   /**
    * The least distance the generated content keeps from the view's border, per
-   * side, as a css length (e.g. `"3mm"`). An omitted side keeps the inset the
-   * view already has; a given side raises it, never lowers it.
+   * side, as a css length (e.g. `"3mm"`). A given side raises the inset the
+   * view already has, never lowers it.
    */
   minContentMargin?: {
     top?: string;