Fast css fixes

[philippjfr]

Fixes #3426
Fixes #3430
Fixes #3437

[codecov]

Codecov Report

Merging #3464 (8e6d1c8) into master (aa2bf86) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3464      +/-   ##
==========================================
- Coverage   83.15%   83.14%   -0.02%     
==========================================
  Files         199      199              
  Lines       27077    27071       -6     
==========================================
- Hits        22516    22508       -8     
- Misses       4561     4563       +2     

Impacted Files	Coverage Δ
panel/io/reload.py	69.56% <0.00%> (-2.18%)	⬇️
panel/tests/command/test_serve.py	83.54% <0.00%> (-1.46%)	⬇️
panel/io/server.py	78.04% <0.00%> (-0.22%)	⬇️
panel/io/state.py	70.38% <0.00%> (-0.22%)	⬇️
panel/pane/idom.py	27.40% <0.00%> (+0.20%)	⬆️
panel/io/callbacks.py	72.99% <0.00%> (+0.52%)	⬆️

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