I think dark mode was a harbinger of dumbed down UI. Instead of spending time on one good UI, designers and developers were forced to make 2 mediocre ones instead. Plus dark mode is easier if you remove all detail and depth from control elements.
That's kind of my whole point. Dark mode features are a symptom of UIs that no longer communicate anything significant with color and shade so just changing color with CSS tweaks doesn't break them.
New GitHub looks alright on low resolutions, but looks kinda awful on big screens. This is the opposite problem old GitHub had.
Though you seem to be suggesting that's somehow a bad thing and I'm not sure why. Dark mode is so popular that operating systems have even started supporting a native toggle.