I'm trying Citizen as a default for my site and infoboxes are getting cut off from the side on mobile. Also some of the subheadings colors need to be updated for dark. e.g. https://encyc.org/wiki/World_War_II It works fine with MinervaNeue.
Topic on Skin talk:Citizen
MinervaNeue comes with some opinionated styles override for infobox specifically, and Citizen doesn't do it for compatibility reasons.
As for dark mode and the responsiveness, since it is a custom template, it should be handled on the wiki through CSS.
https://github.com/StarCitizenTools/mediawiki-skins-Citizen/wiki/Using-Citizen-styles might help