css: handle top-level semicolons in parser

src/browser/css/Parser.zig

@@ -318,12 +318,6 @@ pub const RulesIterator = struct {
         var selector_start: ?usize = null;
         var selector_end: ?usize = null;
 
-        // Skip leading trivia
-        while (self.stream.peek()) |peeked| {
-            if (!isWhitespaceOrComment(peeked.token)) break;
-            _ = self.stream.next();
-        }
-
         while (true) {
             const peeked = self.stream.peek() orelse return null;
 
@@ -370,6 +364,11 @@ pub const RulesIterator = struct {
                 continue;
             }
 
+            if (selector_start == null and (isWhitespaceOrComment(peeked.token) or isSemicolon(peeked.token))) {
+                _ = self.stream.next();
+                continue;
+            }
+
             const span = self.stream.next() orelse return null;
             if (!isWhitespaceOrComment(span.token)) {
                 if (selector_start == null) selector_start = span.start;
@@ -470,3 +469,13 @@ test "RulesIterator: comments and whitespace" {
     try testing.expectEqualStrings(" /* comment */ color: red; ", rule.block);
     try testing.expectEqual(@as(?Rule, null), it.next());
 }
+
+test "RulesIterator: top-level semicolons" {
+    var it = RulesIterator.init("*{}; ; p{}");
+    var rule = it.next() orelse return error.MissingRule;
+    try testing.expectEqualStrings("*", rule.selector);
+
+    rule = it.next() orelse return error.MissingRule;
+    try testing.expectEqualStrings("p", rule.selector);
+    try testing.expectEqual(@as(?Rule, null), it.next());
+}

src/browser/tests/css/stylesheet.html

@@ -468,6 +468,18 @@
 }
 </script>
 
+<script id="CSSStyleSheet_insertRule_semicolon">
+{
+    const style = document.createElement('style');
+    document.head.appendChild(style);
+    const sheet = style.sheet;
+
+    // Should not throw even with trailing semicolon
+    sheet.insertRule('*{};');
+    testing.expectEqual(1, sheet.cssRules.length);
+}
+</script>
+
 <script id="CSSStyleSheet_replaceSync">
 {
     const sheet = new CSSStyleSheet();