visual (CSS) distinction of qa/prod environment

[arubdesu]

Please let me work on this feature, but we'd like to make a qa deployment visually distinctive to know which environment we're working in. I'm assuming this is ok to be exposed in base.json and would just be a logic path to tell CSS/bootstrap to assign a distinct color e.g. to the header. Coworker might help me with dark mode on the way, but going to see if simpler task can be accomplished first, may not be for a few months, just recording for now.