Refactor code

[alexander-akait]

Support PostCSS 8 + refactor

[codecov-commenter]

Codecov Report

Merging #26 into master will decrease coverage by 0.49%.
The diff coverage is 98.00%.

@@            Coverage Diff             @@
##           master      #26      +/-   ##
==========================================
- Coverage   99.00%   98.51%   -0.50%     
==========================================
  Files           2        1       -1     
  Lines         301      269      -32     
  Branches       96       92       -4     
==========================================
- Hits          298      265      -33     
- Misses          3        4       +1     

Impacted Files	Coverage Δ
src/index.js	98.51% <98.00%> (ø)

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