I don’t really know anything about CSS so it’s not really useable for me, which is why the bounty is still out if someone can help me get it to work out on my site.
This is as close as I got to a dark theme so far: https://meta.discourse.org/t/css-theme-for-hub-jmonkeyengine-org/24468
But want this mainly: https://meta.discourse.org/t/a-more-robust-ecosystem-for-creating-sharing-and-modifying-themes/24402/4