As you can know, now Codeforces only have a boring white theme, and that's it. My opinion is that we should at least give us a choice that can change the theme to dark mode so it could be better for learners that work at night. Even better, I suggest adding a choice where we can customize our background with images!
If you have any idea, write the source in here for me to read them
Just download the dark reader extension if it bothers you so much.
if you are using Google chrome you can use chrome://flags/#enable-force-dark to enable dark mode (this causes most/all websites to be in dark mode)
Suggest using tampermonkey to customize styles if you need professional adjust.