There is very little documentation for how to customize the CSS on Mastodon.
One example is here, and the author also had trouble finding good examples. https://battlepenguin.com/tech/using-custom-css-with-mastodon/
This repo contains an example of how to adjust the look of Mastodon to use a new color scheme, without introducing a theme.
At this time there is only CSS for the dark theme. It seems likely that minor changes to Mastodon could affect the CSS. I had to poke around with browser developer tools to fix a few things. To minimize issues, always test changes using a development Mastodon instance.
Feedback welcome!
Log in as administrator, and edit the CSS to your liking and then paste into the tab at
Administration > Server Settings > Appearance
// as root. phased restart w zero downtime
$ systemctl reload mastodon-web
That's all folks!