Update CSS to reduce layout shifts & improve compatibility

[swissspidy]

Fixes #945

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (910d4f1) 97.00% compared to head (a2adce6) 100.00%.

❗ Current head a2adce6 differs from pull request most recent head 86faa0d. Consider uploading reports for the commit 86faa0d to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #947      +/-   ##
===========================================
+ Coverage   97.00%   100.00%   +2.99%     
===========================================
  Files           5         4       -1     
  Lines         601       178     -423     
  Branches       39        39              
===========================================
- Hits          583       178     -405     
+ Misses         18         0      -18     

Flag	Coverage Δ
default	?
js	100.00% <ø> (ø)
multisite	?

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