Do you use the UserStyles/Stylus theme? I think you might do - you posted this 23d ago and I last updated it on the 11th of December.
I made the RPS in Pieces theme, and when I came back to use the forums for the RPS Advent Calendar Guessing Game I finally got around to giving the forum CSS a pass-over. You can always check when and what I’ve updated on the theme’s UserStyles page: https://userstyles.org/styles/162650/rps-in-pieces-new-dark-mode
I noticed the avatar issue earlier today as well, unfortunately it’s not something I can fix in CSS (though I could with a GreaseMonkey script, and I was considering writing one to replace images on the main site with their full quality versions because the artefacting bugs the hell out of me).
I quite like the low contrast grey-on-grey edit box but if you feel it is too unreadable I could increase it.
Changes still to make: buttons at bottom of threads, buttons underneath timeline slider, buttons at bottom of post on moueover, smiley popup by edit box, visited link colour, notification panel, quote popup when text highlighted, profile activity page.