My hope is that is is something Samuel is working on.
I’ve looked at the CSS, considering trying to port the dark colour palette from mobile to web but even after filtering out anything not related to colours there are over 2700 lines of CSS with over 400 unique colours (well, probably a bit less, there are mixed rgba and hex colours).
Judging by Splike’s userstyle you don’t have to touch a lot of that but for an official solution you’d probably want to…