Convert CSS files to Sass

[it-vegard]

Explanation

The current implementation makes heavy use of native CSS variables. Unfortunately, IE does not support this, and probably never will. It would, of course, be nice to forget all about IE, but for various reasons, like corporate policy or support for assistive technology, IE is still used quite a bit. So, we need to fix this.

Suggested solution

To keep using variables, I suggest converting to Sass, and using Sass variables.
We have to stop using CSS Variables in JS, which will require a bit of re-writing, but it shouldn't be too time-consuming.