webapi: (minor) CSS WebApi should be called "CSS" not "Css"

src/browser/tests/window/to_string_tag.html

@@ -9,6 +9,7 @@
     testing.expectEqual("[object HTMLDivElement]", Object.prototype.toString.call(HTMLDivElement.prototype));
     testing.expectEqual("[object HTMLDivElement]", Object.prototype.toString.call(document.createElement("div")));
     testing.expectEqual("[object HTMLUnknownElement]", Object.prototype.toString.call(document.createElement("bogus")));
+    testing.expectEqual("[object CSS]", Object.prototype.toString.call(CSS));
 </script>
 
 <script id=tag_descriptors>

src/browser/webapi/CSS.zig

@@ -206,6 +206,7 @@ pub const JsApi = struct {
 
     pub const Meta = struct {
         pub const name = "Css";
+        pub const class_string = "CSS";
 
         // Per the CSSOM spec, CSS is a namespace object — members are own
         // properties so Object.entries(CSS) returns them.