LibWeb: Make -webkit-appearance an alias for the appearance css property

Author: https://github.com/bplaat
Commit: 44ff957784
Pull-request: https://github.com/SerenityOS/serenity/pull/22370

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -395,6 +395,8 @@ static void set_property_expanding_shorthands(StyleProperties& style, CSS::Prope
             return PropertyID::Left;
         case PropertyID::InsetInlineEnd:
             return PropertyID::Right;
+        case PropertyID::WebkitAppearance:
+            return PropertyID::Appearance;
         default:
             return {};
         }