Swap style rule with utility class

app/assets/stylesheets/pages/projects.scss

@@ -59,10 +59,6 @@
   }
 }
 
-.classification-label {
-  background-color: $red-500;
-}
-
 .toggle-wrapper {
   margin-top: 5px;
 }

app/views/layouts/nav/_classification_level_banner.html.haml

 - if ::Gitlab::ExternalAuthorization.enabled? && @project
   = content_for :header_content do
-    %span.badge.color-label.classification-label.has-tooltip{ title: s_('ExternalAuthorizationService|Classification label') }
+    %span.badge.color-label.gl-bg-red-500.has-tooltip{ title: s_('ExternalAuthorizationService|Classification label') }
       = sprite_icon('lock-open', size: 8, css_class: 'inline')
       = @project.external_authorization_classification_label