Does anyone have some CSS for that? Thanks.
Topic on Skin talk:Minerva Neue
Seems there is no Dark Mode for hte Minerve_Neue skin yet, but there seems to be two for the Timeless skin (for example https://www.mediawiki.org/wiki/Skin:Timeless-DarkCSS although I couldn't make it work yet on my wiki) so you may want to use that one instead (IMO it is offer way better functions than Minerva_Neue).
If wfLoadSkin( 'Timeless' ); throws an error on your wiki, be sure to add $wgMFDefaultSkinClass = "SkinTimeless"; to your LocalSettings.php as well.
https://phabricator.wikimedia.org/T206094 has some code you can try.