Apply light mobile header and border styles

[at-susie]

Description

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% :warning:

Comparison is base (6d19d70) 93.99% compared to head (e7bbecf) 93.99%. Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1568      +/-   ##
==========================================
- Coverage   93.99%   93.99%   -0.01%     
==========================================
  Files         644      648       +4     
  Lines       17381    17459      +78     
  Branches     5702     5710       +8     
==========================================
+ Hits        16338    16411      +73     
- Misses        974      979       +5     
  Partials       69       69              

Files Changed	Coverage Δ
src/app-layout/visual-refresh/background.tsx	85.71% <ø> (ø)
src/app-layout/visual-refresh/header.tsx	100.00% <ø> (ø)
src/app-layout/visual-refresh/index.tsx	100.00% <ø> (ø)
src/app-layout/visual-refresh/navigation.tsx	100.00% <ø> (ø)
src/app-layout/visual-refresh/tools.tsx	83.33% <ø> (-3.56%)	:arrow_down:
src/app-layout/visual-refresh/mobile-toolbar.tsx	100.00% <100.00%> (ø)

... and 12 files with indirect coverage changes

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[at-susie]

This PR is only for experimental prototype.