Convert stylesheets to use css custom properties

[edwardloveall]

Supporting #2732

This converts all sass color variables (and a couple other variables) to use native css variables instead.

There's a lot here! If you'd prefer, I can figure out how to break this up into smaller parts; maybe one per var or something. It also doesn't get rid of all sass variables. I could go even farther and do that if we want. Just let me know.

[nickcharlton]

Thanks! Yeah, it's a bit big!

It also doesn't get rid of all sass variables. I could go even farther and do that if we want.

…have you seen a path to removing Sass entirely? That'd be fun.

[edwardloveall]

Thanks! Yeah, it's a bit big!

Cool, I'll work on breaking it up.

…have you seen a path to removing Sass entirely? That'd be fun.

I think so. I haven't done a full audit or anything but css has come a long way. I think the blocking factor would be which old browsers does administrate need to support.

[edwardloveall]

Alright here's a start with a much smaller scope. I see two ways forward:

• I ship just this PR and follow up with about 20 (give or take 10) of a similar size converting a couple vars at a time.
• I keep going on this branch so it's one var per commit until we've done em all, but at least you can review one commit at a time.

Preference? I lean toward the one branch thing since it's less branch juggling for me, but you probably have more to keep track of as maintainer so I think this is up to you.