diff --git a/packages/core/lib/src/internal/ops/tag_font.dart b/packages/core/lib/src/internal/ops/tag_font.dart
index d4a7229cb..09fcc3103 100644
--- a/packages/core/lib/src/internal/ops/tag_font.dart
+++ b/packages/core/lib/src/internal/ops/tag_font.dart
@@ -9,6 +9,7 @@ const kCssFontFamily = 'font-family';
 
 const kCssFontSize = 'font-size';
 const kCssFontSizeXxLarge = 'xx-large';
+const kCssFontSizeXxxLarge = 'xxx-large';
 const kCssFontSizeXLarge = 'x-large';
 const kCssFontSizeLarge = 'large';
 const kCssFontSizeMedium = 'medium';
diff --git a/packages/core/lib/src/internal/text_ops.dart b/packages/core/lib/src/internal/text_ops.dart
index ab2c9bd0f..b0c8cc3d6 100644
--- a/packages/core/lib/src/internal/text_ops.dart
+++ b/packages/core/lib/src/internal/text_ops.dart
@@ -75,6 +75,8 @@ double? _fontSizeTryParseCssLength(InheritedProperties resolved, CssLength v) =>
 
 double? _fontSizeTryParseTerm(InheritedProperties resolved, String value) {
   switch (value) {
+    case kCssFontSizeXxxLarge:
+      return _fontSizeMultiplyRootWith(resolved, 3.0);
     case kCssFontSizeXxLarge:
       return _fontSizeMultiplyRootWith(resolved, 2.0);
     case kCssFontSizeXLarge:
diff --git a/packages/core/test/core_test.dart b/packages/core/test/core_test.dart
index 2bb54047e..b6815c6fc 100644
--- a/packages/core/test/core_test.dart
+++ b/packages/core/test/core_test.dart
@@ -1131,6 +1131,12 @@ void main() {
       expect(explained, equals('[RichText:(@8.3:Foo)]'));
     });
 
+    testWidgets('renders xxx-large', (WidgetTester tester) async {
+      const html = '<span style="font-size: xxx-large">Foo</span>';
+      final explained = await explain(tester, html);
+      expect(explained, equals('[RichText:(@30.0:Foo)]'));
+    });
+
     testWidgets('renders xx-large', (WidgetTester tester) async {
       const html = '<span style="font-size: xx-large">Foo</span>';
       final explained = await explain(tester, html);