I’ve already splashed this around the facebook groups but I haven’t seen it here yet, and not everybody likes fb~
So dark mode themes are now in beta on github, hopefully (due to their A/B rollout practices) you already have it too. Check either of these places (profile or settings):
I’m glad for this, because this was one of the last hold-outs for doing it. I had tampermonkey installed with user theme scripts to give me dark mode before now anyway, but it wasn’t perfect, would break, and why run an extension/plugin if you don’t really need to. So now I’m extension-free in my browser and have things looking the way I want.