fix: Inline !important styles being overwritten by stylesheet !important styles

Signed-off-by: Dmitry Dygalo <dmitry@dygalo.dev>

Author: Stranger6667

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 ### Added

bindings/c/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 ### Added

bindings/java/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 ### Added

bindings/javascript/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.1] - 2025-12-29
 
 ### Fixed

bindings/php/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 - Initial public release

bindings/python/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 ### Added

bindings/ruby/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Inline `!important` styles being overwritten by stylesheet `!important` styles. [#637](https://github.com/Stranger6667/css-inline/issues/637)
+
 ## [0.19.0] - 2025-12-29
 
 ### Added

css-inline/src/html/serializer.rs

@@ -557,11 +557,14 @@ fn merge_styles<Wr: Write>(
                 }),
         ) {
             // The new rule is `!important` and there's an existing rule with the same name
-            // In this case, we override the existing rule with the new one
+            // Only override if the existing inline rule is NOT `!important`.
+            // Per CSS spec: inline `!important` takes precedence over stylesheet `!important`
             (Some(value), Some(buffer)) => {
-                // We keep the rule name and the colon-space suffix - '<rule>: `
-                buffer.truncate(property.len().saturating_add(STYLE_SEPARATOR.len()));
-                write_declaration_value(buffer, value)?;
+                if !buffer.ends_with(b"!important") {
+                    // We keep the rule name and the colon-space suffix - '<rule>: `
+                    buffer.truncate(property.len().saturating_add(STYLE_SEPARATOR.len()));
+                    write_declaration_value(buffer, value)?;
+                }
             }
             // There's no existing rule with the same name, but the new rule is `!important`
             // In this case, we add the new rule with the `!important` suffix removed

css-inline/tests/test_inlining.rs

@@ -291,6 +291,18 @@ fn important_more_specific() {
     );
 }
 
+#[test]
+fn important_inline_wins_over_stylesheet_important() {
+    // Inline `!important` rules should override stylesheet `!important` rules.
+    // Per CSS spec: "Inline important styles take precedence over all other important author styles"
+    // See: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/important#inline_styles
+    assert_inlined!(
+        style = "h1 { color: blue !important; }",
+        body = r#"<h1 style="color: red !important;">Big Text</h1>"#,
+        expected = r#"<h1 style="color: red !important">Big Text</h1>"#
+    );
+}
+
 #[test]
 fn font_family_quoted() {
     // When property value contains double quotes