Fix class hierarchy elements taking too much vertical space

[tristanlatr]

Just a small css change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.61%. Comparing base (7e0a09f) to head (758d1b9).

❗ Current head 758d1b9 differs from pull request most recent head 9de3d82. Consider uploading reports for the commit 9de3d82 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #785      +/-   ##
==========================================
- Coverage   92.65%   92.61%   -0.04%     
==========================================
  Files          47       47              
  Lines        8373     8373              
  Branches     1844     1844              
==========================================
- Hits         7758     7755       -3     
- Misses        354      356       +2     
- Partials      261      262       +1     

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[github-actions]

According to pydoctor_primer, this change doesn't affect pydoctor warnings on a corpus of open source code. ✅