LibHTML: Implement basic style inheritance

Author: https://github.com/bugaevc
Commit: 841ae44392
Pull-request: https://github.com/SerenityOS/serenity/pull/609
Reviewed-by: https://github.com/awesomekling ✅

Libraries/LibHTML/CSS/StyleResolver.h

@@ -18,7 +18,7 @@ public:
     Document& document() { return m_document; }
     const Document& document() const { return m_document; }
 
-    StyleProperties resolve_style(const Element&);
+    StyleProperties resolve_style(const Element&, const StyleProperties* parent_properties) const;
 
     NonnullRefPtrVector<StyleRule> collect_matching_rules(const Element&) const;