After the KSP forum switch to the new IPS software, many people seemed to not like the all-white background, with ligh-grey text.
Forum user n.b.z was awesome enough to make a Dark Blue forum theme, useable with the Stylish addon. He wrote the over 1200 lines of code for this, so please give him some rep by liking his post, and give him a "Thank You" post, as well:
I prefer REALLY dark, mostly black themes, and n.b.z was kind enough to give permission for me to tweak his theme.
This is my clumsy version of that theme.
Relevant Links:
Pics: https://imgur.com/a/eLpXv
Stylish (browser plugin) homepage, and submitted "user styles":
Direct link for my Darkblue KSP Forum theme:
https://userstyles.org/styles/128030/darkblack-ksp-forum
Other KSP Forum themes for Stylish:
https://userstyles.org/styles/browse?search_terms=kerbal
A few relevant, very informative KSP Forum threads on changing/customizing your own themes, and how n.b.z wrote his Stylish theme, which can be "customized" by any one:
LICENSE: CC0 1.0 Universal (CC0 1.0) Public Domain https://creativecommons.org/publicdomain/zero/1.0/