[BD-46] fix: skeleton.css for both dev and prod

[monteri]

Description

The issue was that in the prod environment Skeleton didn't show up. The fix is to use @use instead of @import.
#2420

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[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (b77488e) 91.65% compared to head (3495ab8) 91.65%.
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2531   +/-   ##
=======================================
  Coverage   91.65%   91.65%           
=======================================
  Files         236      236           
  Lines        4195     4195           
  Branches     1012     1012           
=======================================
  Hits         3845     3845           
  Misses        346      346           
  Partials        4        4           

see 2 files with indirect coverage changes

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[PKulkoRaccoonGang]

@adamstankiewicz @monteri checked for performance in the MFE frontend-app-course-authoring

[adamstankiewicz]

@adamstankiewicz @monteri checked for performance in the MFE frontend-app-course-authoring

Great, thanks! I've also verified this change on my machine locally with the Paragon repo (docs site + example MFE) and the frontend-template-application MFE (npm start & npm run build) as well. Seems like we have sufficient confidence with this change to merge.

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[edx-semantic-release]

🎉 This PR is included in version 21.1.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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