LibWeb: Parse the CSS scrollbar-width property

Author: https://github.com/kalenikaliaksandr
Commit: 8d9e20cb03
Pull-request: https://github.com/SerenityOS/serenity/pull/23381
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibWeb/CSS/StyleProperties.h

@@ -158,6 +158,8 @@ public:
 
     QuotesData quotes() const;
 
+    Optional<CSS::ScrollbarWidth> scrollbar_width() const;
+
     static NonnullRefPtr<Gfx::Font const> font_fallback(bool monospace, bool bold);
 
 private: