fix type check: case-insensitive, accept empty string, clear on disconnect

Per spec, valid type values are absent, empty string, or a
case-insensitive match for "text/css". Also clear cached sheet
when the element is disconnected or type becomes invalid.

src/browser/tests/element/html/style.html

@@ -19,6 +19,25 @@
     lessStyle.type = 'text/less';
     document.head.appendChild(lessStyle);
     testing.expectEqual(null, lessStyle.sheet);
+
+    // Empty type attribute is valid (defaults to text/css per spec)
+    const emptyType = document.createElement('style');
+    emptyType.setAttribute('type', '');
+    document.head.appendChild(emptyType);
+    testing.expectEqual(true, emptyType.sheet instanceof CSSStyleSheet);
+
+    // Case-insensitive type check
+    const upperType = document.createElement('style');
+    upperType.type = 'TEXT/CSS';
+    document.head.appendChild(upperType);
+    testing.expectEqual(true, upperType.sheet instanceof CSSStyleSheet);
+
+    // Disconnection clears sheet
+    const tempStyle = document.createElement('style');
+    document.head.appendChild(tempStyle);
+    testing.expectEqual(true, tempStyle.sheet instanceof CSSStyleSheet);
+    document.head.removeChild(tempStyle);
+    testing.expectEqual(null, tempStyle.sheet);
   }
 </script>
 

src/browser/webapi/element/html/Style.zig

@@ -79,8 +79,17 @@ pub fn setDisabled(self: *Style, disabled: bool, page: *Page) !void {
 const CSSStyleSheet = @import("../../css/CSSStyleSheet.zig");
 pub fn getSheet(self: *Style, page: *Page) !?*CSSStyleSheet {
     // Per spec, sheet is null for disconnected elements or non-CSS types.
-    if (!self.asNode().isConnected()) return null;
+    // Valid types: absent (defaults to "text/css"), empty string, or
-    if (!std.mem.eql(u8, self.getType(), "text/css")) return null;
+    // case-insensitive match for "text/css".
+    if (!self.asNode().isConnected()) {
+        self._sheet = null;
+        return null;
+    }
+    const t = self.getType();
+    if (t.len != 0 and !std.ascii.eqlIgnoreCase(t, "text/css")) {
+        self._sheet = null;
+        return null;
+    }
 
     if (self._sheet) |sheet| return sheet;
     const sheet = try CSSStyleSheet.init(page);