Fix import-map-overrides dialog style

[ryan-pratt]

They changed to putting everything in the shadow DOM, which means we can't style it directly from our stylesheets anymore. Dialog text was unreadable due to it using the default color: canvastext; from the user-agent sheet for dialogs, which is rgb(255,255,255). I think their demo still works because of differing themes.

Before:

After:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
100.0% Duplication on New Code

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.40%. Comparing base (48a3666) to head (ad965bd).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1880      +/-   ##
==========================================
- Coverage   79.40%   79.40%   -0.01%     
==========================================
  Files         523      523              
  Lines       40905    40905              
==========================================
- Hits        32482    32479       -3     
- Misses       8423     8426       +3     

Flag	Coverage Δ
python	83.97% <ø> (-0.03%)	⬇️
ruby-api	48.45% <ø> (ø)
ruby-backend	82.51% <ø> (ø)

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