Thanks for your help, Daeraxa!
I found the problem: Dark theme. I got the CSS you linked working in light theme (as it states in the headline mentioned in the link).
When I switch back to dark mode, my text is all white (on black background) again. How can I get it working for dark theme? I don't get why it's not working for dark mode, is it other CSS classes then?
Also, do you know how I can change list item indent?
Thanks!