Override global Sass variables from theme

Dev
3

As a wise man once said:

I can’t see much use for this beyond colours, and I can’t ever see a user wanting to enable two themes both of which change the color scheme.

Perhaps though this makes more sense as an extension to color_schemes, which can only be enabled individually:

"color_schemes": {
  "Extened Scheme": {
    "primary": "000",
    "primary-medium": "666",
    "primary-low": "aaaaaa"
  }
}