That’s because you are trying with a locked version. Ideally for any new changes @ STAN, you need to copy a Good version (published – eg. Stage 7.9 @ wl6) & once created access that version to make the required changes, be it CSS changes or any other changes like route update, text changes, etc. We can talk more about it when we talk next time.
Regarding this particular request, we are done from both end (CSS by Engkarat & Config’s for INF preferences being hidden) @ Prod.