fix: compatibility with built-in CSS support

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Breaking Changes

Additional Info

webpack/webpack#17223

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.21 🎉

Comparison is base (d2516c4) 90.33% compared to head (88d6411) 90.54%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1035      +/-   ##
==========================================
+ Coverage   90.33%   90.54%   +0.21%     
==========================================
  Files           5        5              
  Lines         838      857      +19     
  Branches      229      243      +14     
==========================================
+ Hits          757      776      +19     
  Misses         71       71              
  Partials       10       10              

Impacted Files	Coverage Δ
src/index.js	96.13% <100.00%> (ø)
src/loader.js	90.10% <100.00%> (+1.08%)	⬆️

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