LibWeb: Implement HTMLStyleElement.sheet

Userland/Libraries/LibWeb/HTML/HTMLStyleElement.cpp

@@ -144,4 +144,11 @@ void HTMLStyleElement::update_a_style_block()
         sheet.release_nonnull());
 }
 
+// https://drafts.csswg.org/cssom/#dom-linkstyle-sheet
+RefPtr<CSS::CSSStyleSheet> HTMLStyleElement::sheet() const
+{
+    // The sheet attribute must return the associated CSS style sheet for the node or null if there is no associated CSS style sheet.
+    return m_associated_css_style_sheet;
+}
+
 }

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;

Userland/Libraries/LibWeb/HTML/HTMLStyleElement.idl

@@ -4,4 +4,7 @@ interface HTMLStyleElement : HTMLElement {
 
     [Reflect] attribute DOMString type;
 
+    // FIXME: This should come from a LinkStyle mixin
+    readonly attribute CSSStyleSheet? sheet;
+
 };