Allow changing colors via SCSS variables

[janbuchar]

What issue does this pull request resolve?

The scss file uses non-default variables for configuration. Unfortunately, these cannot be changed from the outside. This PR aims to change this.

What changes did you make?

The variables were made default and renamed to avoid collisions (I added a rbt- prefix).

Is there anything that requires more attention while reviewing?

I'm aware of no such thing.

[codecov]

Codecov Report

Merging #613 (92fee77) into master (6b9ba84) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #613   +/-   ##
=======================================
  Coverage   99.84%   99.84%           
=======================================
  Files          44       44           
  Lines         661      661           
  Branches      134      134           
=======================================
  Hits          660      660           
  Misses          1        1           

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[coveralls]

Coverage remained the same at 99.849% when pulling 92fee77 on iterait:master into 6b9ba84 on ericgio:master.

[ericgio]

Hey @Teyras, thanks for submitting this PR! Looks like a useful change. Before I merge, do you see any reason why this wouldn't be completely backwards compatible?

[janbuchar]

@ericgio To my best knowledge, there shouldn't be any BC breaks, except maybe some obscure scss manipulation such as manipulating the styles as raw text during the build process (but BC guarantees usually don't extend to such use cases).

Also, someone might rely on the stylesheet to override variables, but that sounds unlikely, too.