Support CSS variables

[geoffrey-eisenbarth]

Discussion on the discord seemed to support this idea (with support from Carson), using the following syntax:

set --variable to value

[1cg]

looks doable, but a little hacky:

https://stackoverflow.com/questions/41370741/how-do-i-edit-a-css-variable-using-js

[geoffrey-eisenbarth]

I would like to take a stab at a PR for this, but it might be post NYE before I can get to it.

[1cg]

Seems like it should support scoping of some kind:

https://blog.logrocket.com/css-variables-scoping/

[1cg]

maybe

  set --variable of :root to value

to do this we'll likely need to change the lexer to recognize a double dash followed by an alpha as a single token of a new type, and then make it act like a property.

We should also add :root to the hyperscript zoo so that will work as a property reference w/o messing w/ the parser.

[1cg]

https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties