User blog comment:Brandon Rhea/Introducing Unification, FANDOM's next big initiative/@comment-27612373-20181002230522/@comment-20644-20181008223833

Given that it's pretty key to the MediaWiki experience, CSS and JS is still allowed with Unification. It's just a matter of where it's allowed through the customization policy, as has been the case for a long time now.

One goal we also have is to provide a Theme Designer that provides the right tools to where it limits the need for CSS in general, mostly so new founders and admins don't need to learn code in order to design their wikis even while code is still an option for them.

Our Design team is currently in the early stages of working on a new Theme Designer that covers all parts of the site (not just wikis on desktop) so this is something we'll be able to talk about more moving forward.