Though I'm always in for Dark-Mode/Night-Mode as I feel that many/most websites would be much easier on the eyes as well as making the text information pop out (so to speak) as well.
"My opinion" would be that I don't feel that this idea is a bad one at all and maybe it's on the WikiTree "Geek Squad" Teams to-do list, it is likely not a high priority in nature.
With that stated...
Many Browsers (like Chrome, Firefox, Waterfox, etc...) have the ability to use optional extensions, addons, etc... that allows for this Dark style feature that's very effective and some are even customizable (in one or more ways) that does work for many individuals on WikiTree.
I support this feature, but I hope that the above information, option, suggestion, etc... was explained okay via text.
Good Luck! :-)