lAs a byproduct of the legacy themes refactor, most of the theme styles now (well, after closing the blocking ticket) work in the editor. This was not the primary goal of that ticket, but since the editor mostly uses the same CSS as the front end, this just worked with minimal effort (correct a few wrong names and small bit of JS to set the variables to the right values).

So there's still a handful of things left in the editor that require additional CSS in the editor overrides.

Created it as low priority because the previous versions of themes didn't get applied at all in the editor and the blocking ticket already improves this situation a lot.