Refactor new layout: responsive course card

[mipyykko]

Originally this was a refactor to named grid areas, but that made the responsive layout a bit annoying to accomplish so I just used flexbox with a bit of container queries. These are only fully supported in the newer browsers, but a polyfill that is conditionally loaded should fix this for the rest.

[codecov]

Codecov Report

Merging #1188 (cd541fa) into master (6e78649) will not change coverage.
The diff coverage is n/a.

❗ Current head cd541fa differs from pull request most recent head 6ad5798. Consider uploading reports for the commit 6ad5798 to get more accurate results

@@           Coverage Diff           @@
##           master    #1188   +/-   ##
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  Coverage   65.51%   65.51%           
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  Files         124      124           
  Lines        5222     5222           
  Branches     1160     1160           
=======================================
  Hits         3421     3421           
  Misses       1677     1677           
  Partials      124      124           

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backend	65.51% <ø> (ø)

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