From 3e9cdb2cf4e42952a28ed40b2d74be5d8dff377d Mon Sep 17 00:00:00 2001
From: Callum Law <callumlaw1709@outlook.com>
Date: Sat, 7 Feb 2026 21:40:54 +1300
Subject: [PATCH] LibWeb: Store whether sheet being parsed is a UA stylesheet

UA stylesheets allow some things that regular stylesheets don't, for
instance allowing use of "non-overridable" `@counter-style` names.
---
 Libraries/LibWeb/CSS/Parser/Parser.cpp | 7 +++++++
 Libraries/LibWeb/CSS/Parser/Parser.h   | 8 ++++++++
 Libraries/LibWeb/CSS/StyleScope.cpp    | 8 ++++----
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Libraries/LibWeb/CSS/Parser/Parser.cpp
index 740e5d128b1..6f913c25b35 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -50,6 +50,12 @@ ParsingParams::ParsingParams(JS::Realm& realm, ParsingMode mode)
 {
 }
 
+ParsingParams::ParsingParams(JS::Realm& realm, IsUAStyleSheet is_ua_style_sheet)
+    : realm(realm)
+    , is_ua_style_sheet(is_ua_style_sheet)
+{
+}
+
 ParsingParams::ParsingParams(DOM::Document const& document, ParsingMode mode)
     : realm(const_cast<JS::Realm&>(document.realm()))
     , document(&document)
@@ -67,6 +73,7 @@ Parser::Parser(ParsingParams const& context, Vector<Token> tokens)
     : m_document(context.document)
     , m_realm(context.realm)
     , m_parsing_mode(context.mode)
+    , m_is_ua_style_sheet(context.is_ua_style_sheet)
     , m_tokens(move(tokens))
     , m_token_stream(m_tokens)
     , m_value_context(move(context.value_context))
diff --git a/Libraries/LibWeb/CSS/Parser/Parser.h b/Libraries/LibWeb/CSS/Parser/Parser.h
index 51c4ed06cc0..289184206f0 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -92,14 +92,21 @@ enum class ParsingMode {
     SVGPresentationAttribute, // See https://svgwg.org/svg2-draft/types.html#presentation-attribute-css-value
 };
 
+enum class IsUAStyleSheet {
+    Yes,
+    No,
+};
+
 struct ParsingParams {
     explicit ParsingParams(ParsingMode = ParsingMode::Normal);
     explicit ParsingParams(JS::Realm&, ParsingMode = ParsingMode::Normal);
+    explicit ParsingParams(JS::Realm&, IsUAStyleSheet);
     explicit ParsingParams(DOM::Document const&, ParsingMode = ParsingMode::Normal);
 
     GC::Ptr<JS::Realm> realm;
     GC::Ptr<DOM::Document const> document;
     ParsingMode mode { ParsingMode::Normal };
+    IsUAStyleSheet is_ua_style_sheet { IsUAStyleSheet::No };
 
     Vector<ValueParsingContext> value_context;
     Vector<RuleContext> rule_context;
@@ -599,6 +606,7 @@ private:
     GC::Ptr<DOM::Document const> m_document;
     GC::Ptr<JS::Realm> m_realm;
     ParsingMode m_parsing_mode { ParsingMode::Normal };
+    IsUAStyleSheet m_is_ua_style_sheet { IsUAStyleSheet::No };
 
     Vector<Token> m_tokens;
     TokenStream<Token> m_token_stream;
diff --git a/Libraries/LibWeb/CSS/StyleScope.cpp b/Libraries/LibWeb/CSS/StyleScope.cpp
index 16653cc8b5d..fa0cc8798e3 100644
--- a/Libraries/LibWeb/CSS/StyleScope.cpp
+++ b/Libraries/LibWeb/CSS/StyleScope.cpp
@@ -142,7 +142,7 @@ static CSSStyleSheet& default_stylesheet()
     static GC::Root<CSSStyleSheet> sheet;
     if (!sheet.cell()) {
         extern String default_stylesheet_source;
-        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), default_stylesheet_source));
+        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm(), Parser::IsUAStyleSheet::Yes), default_stylesheet_source));
     }
     return *sheet;
 }
@@ -152,7 +152,7 @@ static CSSStyleSheet& quirks_mode_stylesheet()
     static GC::Root<CSSStyleSheet> sheet;
     if (!sheet.cell()) {
         extern String quirks_mode_stylesheet_source;
-        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), quirks_mode_stylesheet_source));
+        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm(), Parser::IsUAStyleSheet::Yes), quirks_mode_stylesheet_source));
     }
     return *sheet;
 }
@@ -162,7 +162,7 @@ static CSSStyleSheet& mathml_stylesheet()
     static GC::Root<CSSStyleSheet> sheet;
     if (!sheet.cell()) {
         extern String mathml_stylesheet_source;
-        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), mathml_stylesheet_source));
+        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm(), Parser::IsUAStyleSheet::Yes), mathml_stylesheet_source));
     }
     return *sheet;
 }
@@ -172,7 +172,7 @@ static CSSStyleSheet& svg_stylesheet()
     static GC::Root<CSSStyleSheet> sheet;
     if (!sheet.cell()) {
         extern String svg_stylesheet_source;
-        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), svg_stylesheet_source));
+        sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm(), Parser::IsUAStyleSheet::Yes), svg_stylesheet_source));
     }
     return *sheet;
 }