Or… just stop outputting these empty elements, that are so dumb and bring nothing but problems.

An alternative approach, that makes use of :has() and is much simpler:

Considering there is a mechanism to show such empty elements (wtf, just never outputting the markup of these elements would fix so many issues),
technically the code should be this monstruosity:

p:not(.mw-empty-elt) + table,
.mw-parser-output.mw-show-empty-elt p.mw-empty-elt + table,
body:not(.mw-hide-empty-elt) .mw-parser-output:not(.mw-hide-empty-elt) p.mw-empty-elt + table {
    /* layout "fix" here */
}

We have an issue because of that on frwiki: https://fr.wikipedia.org/wiki/Discussion_mod%C3%A8le:Infobox_V3/S%C3%A9parateur#Mod%C3%A8le_cass%C3%A9

All done, thank you @GMikesell-WMF!

All quite on the wikis so far but I'll leave this open another day in case people who missed the many communications wake up tomorrow to gadgets not working.

I'm moving this ticket back to Ready to be worked on to implement the following revision Nico identified, and we converged on as a team:

We were running the banners between July 10, 11:10 UTC and July 18, 16:40 UTC.

Left a message on https://www.mediawiki.org/wiki/Help_talk:Lint_errors/night-mode-unaware-background-color.

@GMikesell-WMF I can verify this. The URL matches no results, so that's what we're verifying here.

Change #1038911 merged by jenkins-bot:

[mediawiki/core@master] Support mask-image in ResourceLoader ImageModule

https://gerrit.wikimedia.org/r/1038911

@Danielyepezgarces that's unrelated to this issue. Please see T365311 for that issue and workarounds.

Dark mode can be disabled in source mode for eswiki beta testers?

I'm not seeing any issues in production.