CSS vars refactor (#982)

[kkellydesign]

Description

For the first commit of this work, I searched the repo for @supports (css: variables), and refactored those selectors away by replacing the SASS variables in the main selector with their preexisting native CSS equivalent.

Once that was done, I combed through the repo for examples of those SASS variables to make sure I got them all. there were a few that didn't have @supports flags, so I just replaced a handful like this:

$v-grid-md --> var(--v-grid-md)

Finally, I removed all of the SASS variables for grid sizing, font families, and colors. They had all already just been used as duplicate fallbacks for CSS variables, so I'm confident that as long as the SASS compiles, then everything should be consistent.

• I have documented this change in the design system.
• I have recorded this change in CHANGELOG.md.

Issue

982

Testing

Everything compiles, and I gave the app a pretty thorough visual pass compared to the main branch. I'm pretty sure it's all good... but it could benefit from another set of eyes.

[stephaniehobson]

We're going to keep the variable re-factoring until after we've published a version of Protocol that addresses there: #1074

I'll ping you when it's ready for a rebase before it gets a serious review.