LibWeb: Implement HTMLStyleElement.sheet

Author: https://github.com/Lubrsi
Commit: 10d4f2fc1e
Pull-request: https://github.com/SerenityOS/serenity/pull/10282
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibWeb/HTML/HTMLStyleElement.h

@@ -23,6 +23,8 @@ public:
 
     void update_a_style_block();
 
+    RefPtr<CSS::CSSStyleSheet> sheet() const;
+
 private:
     // https://drafts.csswg.org/cssom/#associated-css-style-sheet
     RefPtr<CSS::CSSStyleSheet> m_associated_css_style_sheet;