[CSS] Advanced CSS units

[haikyuu]

It would be useful to make custom CSS units a bit smarter. For example, I'd like to define a gcol unit like so

# doesn't work
global css html 1gcol:repeat(1, minmax(0, 1fr))

# Suggested syntax
global css html 1gcol:repeat($, minmax(0, 1fr))
## This will be used
<span[gtc:12gcol]>

## equivalent to
<span[gtc:repeat(12, minmax(0, 1fr))]>

Using a $ as a placeholder for the unit multiplier is better, since in this example I don't want the 1fr to be interpolated