Add CSS class to scope the refactoring changes

app/helpers/nav_helper.rb

@@ -12,6 +12,7 @@ module NavHelper
   def page_with_sidebar_class
     class_name = page_gutter_class
     class_name << 'page-with-contextual-sidebar' if defined?(@left_sidebar) && @left_sidebar
+    class_name << 'sidebar-refactoring' if Feature.enabled?(:sidebar_refactor, current_user)
     class_name << 'page-with-icon-sidebar' if collapsed_sidebar? && @left_sidebar
     class_name -= ['right-sidebar-expanded'] if defined?(@right_sidebar) && !@right_sidebar