feat: Copy over dark docs theming from osv.dev

[another-rex]

See preview here: https://another-rex.github.io/osv-scanner/

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.91%. Comparing base (61669db) to head (4383f85).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1245      +/-   ##
==========================================
+ Coverage   67.66%   67.91%   +0.25%     
==========================================
  Files         174      174              
  Lines       16721    16835     +114     
==========================================
+ Hits        11314    11434     +120     
+ Misses       4776     4767       -9     
- Partials      631      634       +3     

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