Fix custom.css html escaped (#18824)

app/views/custom_css/show.css.erb

@@ -1,5 +1,5 @@
 <%- if Setting.custom_css.present? %>
-<%= Setting.custom_css %>
+<%= raw Setting.custom_css %>
 
 <%- end %>
 <%- UserRole.where(highlighted: true).select { |role| role.color.present? }.each do |role| %>