Is it possible to have different background images for login page, based on / for each trusted_domains?

[eehmke]

This seems to solve your problem. Have not tested it, though.

[Howto] Individual themes per domain

Nextcloud has a cool theming option to provide a custom style including wallpaper, name, colour, … Is there any option, maybe in the config files to create different theming styles per accessing domain one the same instance? For example: example.com/cloud blue with wallpaper1 anotherexample.org/cloud green with wallpaper2 …