Theming Lemmy.world?

I was just thinking I'd like to make some UI tweaks - I like dark themes but the dark theme is a little hard to parse for me here.

Of course it's always possible to go the user stylesheets route, with something like Tampermonkey or Stylish. But, is there an established best practice already? Do most instances have the same UI, and, if not, how are the differences implemented?

I also think there's probably room for some more niche stuff like RES used to do, but considering Lemmy is open source it might make sense to do some of that against the official repo rather than as another layer on top. Then again that would make adoption less convenient and under user control.