build: sync CSS / TS(JS) values

[davidlj95]

Some values are the same in CSS and JS, though they are specified in two places as those 2 parts are not communicated.

So 2 sources of truth and associated issues with them

[davidlj95]

Could use getPropertyValue to fetch CSS things from JS

But what about SSR in that scenario? 🤔 Well guess that given there's a virtual document accessible, it could work there too 🤷