So I got the container Gitea running and it works, mounted this way:
volumes: - /home/user/docker-data/gitea:/data
According to gitea docs:
Add a CSS file to $GITEA_PUBLIC/public/css/theme-<theme-name>.css. The value of $GITEA_PUBLIC of your instance can be queried by calling gitea help and looking up the value of “CustomPath”. Add <theme-name> to the comma-separated list of setting THEMES in app.ini
Calling the cli and gitea help gives me:
CustomPath: /data/gitea (GITEA_CUSTOM)
/home/user/docker-data/gitea/gitea which follows that
Which I have, and where I put the files in: https://i.imgur.com/GSdYNAr.png .
[ui] DEFAULT_THEME = gitea THEMES = gitea,arc-green,gitea-modern,plex
and I have it to choose from in gitea: https://i.imgur.com/a9BoWI4.png
Only problem is: They do nothing.
On a side note:
The path has changed in Gitea 1.15, there the file needs to be placed in $GITEA_CUSTOM/public/assets/css I have
public/assets/css. Both not working.