I've seen this requested in the general feature requests forum, but I wanted to provide a more specific idea as well as suggest it for cohost plus.
itch.io enables creators who request permission to add custom CSS to their profile/game pages, by entering it into a text box on the customization page. This has lead to some really fantastic looking pages on itch. In the spirit of the old web, it could be fun to have this on cohost as well!
Obviously you'd need some input sanitation, along with a setting to disable it in case users dont want to deal with seeing it.