improvements to design & layout of docs

[neuromusic]

changes: https://spacetx-starfish.readthedocs.io/en/jk-css-improvements/

[neuromusic]

fixes #1861

[codecov-io]

Codecov Report

Merging #1875 into master will decrease coverage by 31.82%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #1875       +/-   ##
===========================================
- Coverage   87.77%   55.95%   -31.83%     
===========================================
  Files         168      168               
  Lines        5785     5785               
===========================================
- Hits         5078     3237     -1841     
- Misses        707     2548     +1841     

Impacted Files	Coverage Δ
starfish/morphology.py	0.00% <0.00%> (-100.00%)	⬇️
...ish/core/imagestack/parser/tilefetcher/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
...fish/core/imagestack/parser/tilefetcher/_parser.py	0.00% <0.00%> (-90.33%)	⬇️
starfish/test/full_pipelines/api/test_dartfish.py	19.67% <0.00%> (-80.33%)	⬇️
starfish/core/spots/DecodeSpots/util.py	20.40% <0.00%> (-79.60%)	⬇️
starfish/test/full_pipelines/api/test_iss_api.py	22.22% <0.00%> (-77.78%)	⬇️
...e/experiment/builder/test/factories/all_purpose.py	22.91% <0.00%> (-77.09%)	⬇️
starfish/core/starfish.py	0.00% <0.00%> (-76.93%)	⬇️
starfish/test/full_pipelines/api/test_merfish.py	23.80% <0.00%> (-76.20%)	⬇️
...ilder/test/structured_formatter/test_single_fov.py	25.71% <0.00%> (-74.29%)	⬇️
... and 85 more

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[mattcai]

Great, it looks so much better now!