LibWeb/CSS: Discard whitespace when parsing comma-separated lists

Author: https://github.com/AtkinsSJ
Commit: 821bf4a289
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6646
Reviewed-by: https://github.com/tcl3

Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp

@@ -186,6 +186,7 @@ Optional<Parser::PropertyAndValue> Parser::parse_css_value_for_properties(Readon
         return {};
     };
 
+    tokens.discard_whitespace();
     auto& peek_token = tokens.next_token();
 
     auto parse_for_type = [&](ValueType const type) -> Optional<PropertyAndValue> {