Personally the white on white theme of The usaco website (not the guide but the official website) makes my retinas scream in agony, and switching tabs feels every single time like opening the curtains first thing in the morning.

So I don't know if this already exists (I certainly didn't find it anywhere), but I created a script for a usaco.org dark theme. It's janky, it's mostly ai generated, but as far as I know there aren't any better options.

The setup is extremely easy and well explained in the website, here's a link for anyone who's interested:

https://greasyfork.org/en/scripts/526910-usaco-org-dark-mode-by-friday-night

And here are some screenshots: