Seems to be nothing but dark mode for various siteshttps://userstyles.world/
https://uso.kkx.one/ (ad/spyware-free mirror of the old userstyles.org, now mutated into a Chrome-only parody)
Swarth + AutoPageColor covers that use case without needing a separate script per site. I miss the days when these styles actually changed the look of the page, I'd love to have more density of fonts and less whitespace for one.