Not really sure whether I like this or not… it kind of rubs me the wrong way, but I do see where he is coming from and how it could be useful.
IMHO there’s a lot better alternatives out there. https://github.com/MicheleBertoli/css-in-js is a fairly extensive overview.
30KB seems pretty insane for what it does. But I generally think CSS-in-JS is a good idea.