feat: Less shaded dark theme colors

[evyncke]

Addressing #9280 by having less shared (dark) colours for ballot positions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.76%. Comparing base (f5df667) to head (c6f4627).
⚠️ Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9335      +/-   ##
==========================================
+ Coverage   88.74%   88.76%   +0.01%     
==========================================
  Files         320      320              
  Lines       41674    41754      +80     
==========================================
+ Hits        36984    37061      +77     
- Misses       4690     4693       +3     

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