TextEditor: Add syntax-highlighting for CSS files

Author: https://github.com/AtkinsSJ
Commit: d2690e551c
Pull-request: https://github.com/SerenityOS/serenity/pull/10563
Reviewed-by: https://github.com/alimpfard ✅

Userland/Applications/TextEditor/MainWidget.h

@@ -116,6 +116,7 @@ private:
     GUI::ActionGroup syntax_actions;
     RefPtr<GUI::Action> m_plain_text_highlight;
     RefPtr<GUI::Action> m_cpp_highlight;
+    RefPtr<GUI::Action> m_css_highlight;
     RefPtr<GUI::Action> m_js_highlight;
     RefPtr<GUI::Action> m_html_highlight;
     RefPtr<GUI::Action> m_gml_highlight;