I have a dark mode on Firefox (or rather automatic, aligning on system dark theme), and I had Dark Vector also. Going back to Vector stops making the pages light grey, but then the background is black, which I find more tiring for the eyes than white.
There is a "Light mode » option at the top right, between Preferences and Watchlist, but it isn't a proper link (screen shot : ).
I prefer the dark grey colours of the Dark Vector apparrance, but I can't seem to have it without having all the other web pages in light theme.
What is strange is it was working fine a few days ago, and now I have either the wrong colours with Dark Vector (), or the pitch black background without it ().
The colours are fine on my preference page (), but not elsewhere on this wiki.