I just made my own solution. https://github.com/dreimer1986/yourname_card_mod/blob/adcd81bc549b781c7b350c0b13a611c0b4f10404/README-script.md
Works fine and because of the way it works it can even change the backgrounds of stuff like settings menu etc. (until you push F5 in there) AND what is not possible anymore, even on the addin with a fix… Sidebar!
Because of the location where I inject it will be very hard to break it with any kind of update.
The solution needs some editing on your theme though. I decided against any strange hackery that sometimes works and sometimes fails in bad side effects, so you need to change some things to transparent background.