theme.css support needs complete rethink

[elmarsto]

There's currently a kind of chicken-egg problem as to when to load custom theme css rules.

• If it loads before the style.css then the style.css clobbers its variables
• It seems to work fine if you load it after style.css with npm run dev but then when running with npm run start, it's as if style.css loaded last

Further R&D required. Possible solution: do ./public/theme.css and have an @import rule in style.css load the theme. (I tried this but coudln't get it working, tho it was late and I was logging off)

[elmarsto]

https://www.youtube.com/watch?v=5AxwaszFbDw