@JScherer-WMF these styles are currently maintained on wiki, so you'll need to bring this up on the Discord channel. We don't have control over them in Vector 2022.
https://en.wikipedia.org/wiki/MediaWiki:Common.css#L-283

In T366725#9864871, @Jdlrobson wrote:

@JScherer-WMF these styles are currently maintained on wiki, so you'll need to bring this up on the Discord channel. We don't have control over them in Vector 2022.
https://en.wikipedia.org/wiki/MediaWiki:Common.css#L-283

Thanks, Jon. Done.

@stjn noted:

Since other places like .wikitable and .catlinks use border-color-base, it would be more beneficial for uniformity to have infoboxes also use the same
And that variable actually gets changed in night mode from #a2a9b1 to #72777d
the problem here is more so that enWP does not have night mode vars in place, compare to
https://ru.wikipedia.org/wiki/Фонд_благосостояния_Турции?useskin=vector-2022&vectornightmode=1
that is from https://ru.wikipedia.org/wiki/MediaWiki:Common.css#L-526

Yeah, I agree on the consistency point. Even though subtle is a better colour for this usecase overall in my opinion, the dark mode base at #72777d would be preferable to the light mode base at #a2a9b1. That would still make a big improvement.

Updating ticket accordingly.

See also T366839: Dark mode: --color-subtle is not dim enough for base vs subtle, but this time for text colors.