feat: Add header styles inclusion

[Lunyachek]

This is backport from master branch - #321

Header styles inclusion like it done in frontend-app-learning - https://github.com/openedx/frontend-app-learning/blob/master/src/index.scss#L7

It can be useful, for example, for the potential using of cookie banner

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (c644da3) to head (e97d078).

Additional details and impacted files

@@                     Coverage Diff                      @@
##           open-release/quince.master      #322   +/-   ##
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  Coverage                      100.00%   100.00%           
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  Files                             110       110           
  Lines                            1079      1079           
  Branches                          159       159           
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  Hits                             1079      1079           

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[arbrandes]

Marking as draft until master is merged.