fix: Adjust dark theme to make range slider more visible

[larseggert]

Fixes #6881

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (02e0d96) 88.80% compared to head (f5ee3aa) 88.80%.
Report is 22 commits behind head on main.

Files	Patch %	Lines
ietf/doc/views_draft.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6885   +/-   ##
=======================================
  Coverage   88.80%   88.80%           
=======================================
  Files         285      285           
  Lines       40374    40374           
=======================================
+ Hits        35853    35856    +3     
+ Misses       4521     4518    -3     

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