LibWeb: Parse anchor() function for inset properties

Author: https://github.com/tcl3
Commit: 1d9e4a6f62
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5691
Reviewed-by: https://github.com/gmta ✅

Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp

@@ -384,6 +384,9 @@ Optional<Parser::PropertyAndValue> Parser::parse_css_value_for_properties(Readon
     if (auto parsed = parse_for_type(ValueType::Paint); parsed.has_value())
         return parsed.release_value();
 
+    if (auto parsed = parse_for_type(ValueType::Anchor); parsed.has_value())
+        return parsed.release_value();
+
     return OptionalNone {};
 }