Will HN ever get a dark theme?

Probably not. One would have to ask dang for an official reason but I suspect it is due to not making changes to the UI. There have not been any significant changes in a very long time.

If using uBlock Origin here [1] are some HN rules I used to change colors and such. Change the color values to match preferences. May not be reachable on some devices

[1] - https://mirror.newsdump.org/hn-ublock-colors-other.txt

This question is asked a lot. And the answer, based on the silence, has always been "No". Either live without it or use one of the hacks others have posted here to get a dark theme in your browser.

What CSS changes would you make to implement device-adaptive dark mode in the HN CSS — that is, honoring the light or dark signal given by the browser? That’s more complex than a simple dark mode patch, and with that change defined as diff, it would present a stronger case for your desires being met by backend pref coding.