Please provide an official CSS file that the community can use to customize the colors. Since you write the CSS files this should not take to long.
Solution to this problem
Can you please add 3-4 color fields in the admin settings panel where one can specify the CSS color codes and the Seafile server applies them on restart. This would simplify everything so much.
Please add this feature to the 6.2 release. As FASTCGI will be removed also this might be a good plus for users to upgrade and go through the effort of changing the server configs.
Here is an example how it's implemented in Nextcloud. Personally I think that entering one color is not enough, as there are several colors for hovering, selecting etc.