[Bug]: background image is 404 in maintenance mode

[derbenx]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

In maintenance mode background comes up as 404 when nextcloud is in a folder. It's been in pretty much every version, since I remember. :P think the updating mode does this too...

it tries to use: https://server.xxx/apps/theming/img/background/kamil-porembinski-clouds.jpg
instead of: https://server.xxx/subdir/apps/theming/img/background/kamil-porembinski-clouds.jpg
It's configured in weblink, under theming with the folder and anywhere else I can think of.

I tried light and dark theme, in case it was one or the other.

Steps to reproduce

1. use nextcloud in a subdir
2. upgrade
3. (or just enable maintenance mode)

Expected behavior

no 404 errors.

Installation method

Community Manual installation with Archive

Nextcloud Server version

29

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

Apache (supported)

Database engine version

MySQL

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

\apps\theming\css\default.css
is hard coded to:
--image-background-default: url('/apps/theming/img/background/kamil-porembinski-clouds.jpg');

This seems to fix it:
--image-background-default: url('../../apps/theming/img/background/kamil-porembinski-clouds.jpg');