Skip whole CSS at-rule blocks in the SVG parser by brace depth

Found while testing crates/svg/src/lib.rs:510-520 (parse_css)

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/svg/src/lib.rs

@@ -510,12 +510,30 @@ fn parse_css(css: &str, sheet: &mut StyleSheet) -> Result<(), Error> {
     let mut rest = css.as_str();
     while let Some(open) = rest.find('{') {
         let sel = rest[..open].trim();
+        if sel.starts_with('@') {
+            // Skip the whole at-rule block, matching nested braces by depth.
+            let mut depth = 0usize;
+            let mut end = None;
+            for (i, c) in rest[open..].char_indices() {
+                match c {
+                    '{' => depth = depth.saturating_add(1),
+                    '}' => {
+                        depth = depth.saturating_sub(1);
+                        if depth == 0 {
+                            end = Some(open + i + 1);
+                            break;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+            let Some(end) = end else { break };
+            rest = &rest[end..];
+            continue;
+        }
         let Some(close) = rest[open..].find('}') else { break };
         let body = &rest[open + 1..open + close];
         rest = &rest[open + close + 1..];
-        if sel.starts_with('@') {
-            continue;
-        }
         let mut decls = parse_decls(body);
         sheet.decls = sheet.decls.saturating_add(decls.len());
         if sheet.decls > MAX_CSS_DECLARATIONS {

crates/svg/src/tests.rs

@@ -422,3 +422,15 @@ fn font_size_percentage_resolves_against_the_parent_font_size() {
         assert!(matches!(shapes[0].2.geom, Geom::Rect { w, .. } if w == expected), "{body}: {:?}", shapes[0].2.geom);
     }
 }
+
+#[test]
+fn at_rule_blocks_are_skipped_by_brace_depth() {
+    let mut sheet = StyleSheet::default();
+    parse_css("@media print { .a{fill:#ff0000} .b{fill:#0000ff} } .c{fill:red}", &mut sheet).unwrap();
+    assert_eq!(sheet.rules.len(), 1);
+    assert_eq!(sheet.rules[0].classes, vec!["c".to_string()]);
+    let mut sheet = StyleSheet::default();
+    parse_css("@media x { @supports y { .c{} } .d{} } .e{fill:red}", &mut sheet).unwrap();
+    assert_eq!(sheet.rules.len(), 1);
+    assert_eq!(sheet.rules[0].classes, vec!["e".to_string()]);
+}