Evergreen builds do not transform CSS variables

[rorticus]

Update to disable css custom properties when not doing a legacy build.

Before:

--my-color: blue;

.myClass {
    color: blue;
    color: var(--my-color);
}

Now,

--my-color: blue;

.myClass {
    color: var(--my-color);
}

[codecov]

Codecov Report

Merging #151 into master will decrease coverage by 0.11%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
- Coverage      56%   55.88%   -0.12%     
==========================================
  Files           8        8              
  Lines         475      476       +1     
  Branches      113      114       +1     
==========================================
  Hits          266      266              
- Misses        209      210       +1

Impacted Files	Coverage Δ
src/base.config.ts	27.96% <0%> (-0.24%)	⬇️

---

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[codecov]

Codecov Report

Merging #151 into master will decrease coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
- Coverage   54.77%   54.67%   -0.11%     
==========================================
  Files          10       10              
  Lines         544      545       +1     
  Branches      125      126       +1     
==========================================
  Hits          298      298              
- Misses        246      247       +1

Impacted Files	Coverage Δ
src/base.config.ts	25.37% <0%> (-0.2%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[agubler]

For the time being we support css vars so for browsers that support it we have the story covered. Long term we should look at this again and stop bullet proofing the vars, but for now closing this.