I am very happy with Nextcloud but today I noticed a big problem after a completely new setup on Ubuntu 16.04. The Theming App does not work for the Login page anymore! The colors do not change on the login page and the logo will not be applied. Unfortunately I can not manually change the theme, because the Nextcloud core is installed via Snap read-only! How do I solve the problem? I can‘t believe that this isn‘t already fixed in version 12.0.4…
I had the same problem. It started after some upgrade where the whole file list was broken (i.e. no CSS). I disabled the theming app to temporarily fix this problem. After a while I re-enabled it and the list was just fine, but I was unable to set an image. Logs weren’t helpful, too.
After some checking I found out, that the URI to refresh the theming css returned a 404 error. A quick check of the code told me that some SCSS couldn’t be parsed. https://github.com/nextcloud/server/issues/7977#issuecomment-359939527 made me find the problem:
Like you, I used to have a custom color set, which somehow got stored with two # instead of just one. To fix this, try to reset the color. If that doesn’t work, you can manually edit the database (like I did). Use
SELECT * FROM PREFIX_appconfig WHERE appid = 'theming' AND configkey = 'color'
to find the correct row and change the configvalue to have just one #