Use Bootstrap utility to set the font size

ee/app/assets/stylesheets/pages/billings.scss

@@ -16,10 +16,6 @@
       margin-bottom: 16px;
     }
   }
-
-  h4 {
-    font-size: 20px;
-  }
 }
 
 .billing-plans-alert {

ee/app/views/shared/billings/_billing_plan_header.html.haml

@@ -13,7 +13,7 @@
       .avatar-container.rect-avatar.s96.home-panel-avatar.append-right-default.float-none.mx-auto.mb-4.mt-1.rounded.border
         = group_icon(@group, class: 'avatar avatar-tile s96', width: 96, height: 96, alt: @group.name)
 
-  %h4
+  %h4.h4
     - plan_link = plan.about_page_href ? link_to(plan.code.titleize, plan.about_page_href) : plan.name
     - if namespace == current_user.namespace
       = s_("BillingPlans|@%{user_name} you are currently on the %{plan_link} plan.").html_safe % { user_name: current_user.username, plan_link: plan_link }