With the latest update(s) to the CSS endpoint and/or the Minerva styles themselves, it looks like the ability of the page-library to set the Theme of the article to stop working.
There don't seem to be any javascript errors, so it's a bit difficult to pinpoint where exactly the error lies.
The main problem is that the background of the text itself is not being set correctly, which leads to the following appearance in dark mode:
We are getting a torrent of OTRS feedback about this issue.