Refactor CSS for assistant component: adjust media queries and container widths for better responsiveness

[bendichter]

fix #2123

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.19%. Comparing base (07495a8) to head (3c71b7e).
⚠️ Report is 12 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #2124   +/-   ##
=======================================
  Coverage   95.19%   95.19%           
=======================================
  Files          28       28           
  Lines        2849     2849           
  Branches      736      736           
=======================================
  Hits         2712     2712           
  Misses         83       83           
  Partials       54       54           

Flag	Coverage Δ
integration	74.16% <ø> (ø)
unit	85.08% <ø> (ø)

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[bendichter]

open.asst.demo.mov

[bendichter]

fyi @h-mayorquin

[rly]

Looks great!