Well, this was a thread... but apparently the server got reset. Looks like we've still got the UI changes.
EDIT: To those who haven't seen, @HebaruSan has an excellent Stylish configuration for a forums "Dark Mode". Check it out, it's great!
I've decided to throw my hat into the ring of publicly shared user styles. Use this instead of the spoilered code block, it already has a lot of small fixes since that point:
https://userstyles.org/styles/191139/dark-kerbal-space-program-forum