Fix visual accessibility issues 6 and 20

[peterychang]

Why are these changes needed?

Fixes visual accessibility issues (6) Luminosity contrast ratio of focus indicator on 'Venv' control is less than 3:1. and (20) "Only color is used to indicate the focus indicator on the 'Venv', and 'conda' Tab controls."

Related issue number

#5633

before:

after:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.91%. Comparing base (5615f40) to head (a7f7936).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5725   +/-   ##
=======================================
  Coverage   74.91%   74.91%           
=======================================
  Files         175      175           
  Lines       11137    11137           
=======================================
  Hits         8343     8343           
  Misses       2794     2794           

Flag	Coverage Δ
unittests	74.91% <ø> (ø)

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