Click this button to install the script (a userscript manager like Tampermonkey, Violentmonkey, or Greasemonkey is required): ($Install\ Script-2.5::control ring)
If anyone has any feedback let me know.
I also found an older topic, but this one is much more lightweight.
I've decided to try making a fork/remix of this userscript
mostly did simplification and bugfixes (e.g. dialogs have white text and white background)
Edit: I just made a website for it https://darksnap.swee.codes
Sorry for the sudden necrobump! After 5 months I finally dropped an update to this. It's mostly a huge bug fix update because of some oversights and/or changes that Snap! recently made.
Fixed flash of unstyled content
Fixed the description background on collections, and the notes background on the new project page
Fixed footer trapezoid
Fixed collections without thumbnails saying "collection thumbnail"
I also moved the code from this post over to a git repo so you can get auto-updates and so that it's easier for me to edit the code. If you already have this script, delete it from your userscript manager before installing this new one.