Nextcloud 16.0.4
VPS, running with OpenSuse Leap 15.0, soon 15.1
Apache 2.4.33
PHP 7.2.5
General questions, brainstorming phase, ideas welcome 
Running my NC instance natively installed on my (hosted) VPS. Mainly private usage, family, friends. A few colleagues. Fine for years now, migrated from OC that time, never any serious issues. Great piece of software!!!
For a new group of users, who will access my NC instance via a separate Domain (I’m fine with “trusted_domains”, already using it in different context), it would be “nice-to-have” a different background image on the login page. Rest of theming could stay the same, in fact except the colors it’s NC’s standard.
That’s all
I know from the theming app, that there’s no link between theming and a “trusted_domain”, so I believe having a sep. login page background image is not possible out of the box.
No brainer that I could setup a complete 2nd NC instance, but this would make “life” more complicated for me, as the “admin”: 2 logins, additional calDAV and esp. cardDAV links on mobiles etc. pp.
Any ideas how to get this idea as simple as possible done would be great. If the answer would be “no, not easy”, also fine, as said: nice to have. But really nice 
Sunny weekend wherever you are,
Michael