LibWeb: Update CSSRule parent style sheet whenever parent rule changes

Author: https://github.com/Calme1709
Commit: 89a08cb7cf
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5176
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/CSSRule.cpp

@@ -53,6 +53,11 @@ void CSSRule::set_css_text(StringView)
 void CSSRule::set_parent_rule(CSSRule* parent_rule)
 {
     m_parent_rule = parent_rule;
+
+    if (parent_rule == nullptr)
+        set_parent_style_sheet(nullptr);
+    else
+        set_parent_style_sheet(parent_rule->parent_style_sheet());
     clear_caches();
 }
 

Libraries/LibWeb/CSS/CSSRuleList.cpp

@@ -171,8 +171,8 @@ WebIDL::ExceptionOr<void> CSSRuleList::remove_a_css_rule(u32 index)
     m_rules.remove(index);
 
     // 6. Set old rule’s parent CSS rule and parent CSS style sheet to null.
+    // NOTE: We set the parent stylesheet to null within set_parent_rule.
     old_rule.set_parent_rule(nullptr);
-    old_rule.set_parent_style_sheet(nullptr);
 
     if (on_change)
         on_change();