UI: Fix Visual Focus Indicators aren't visible in high contrast mode

[natainakata]

Closes #25935

What I did

Added indicator display for ActionBar, Input, and Boolean toggle, since it was not clear whether the focus was applied in High Contrast Mode.
Focus on it and the outline will appear.
The Boolean toggle further displays an underscore for the selected boolean value.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

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Probably does not require manual testing.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

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• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

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core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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name	before	after	diff	z	%
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initTime	14.9s	14s	-826ms	-0.63	-5.9%
buildTime	9s	10.5s	1.5s	0.58	14.5%
testBuildTime	0ms	0ms	0ms	-	-
devPreviewResponsive	6.2s	8s	1.8s	0.72	22.6%
devManagerResponsive	4s	5.2s	1.1s	0.85	22.6%
devManagerHeaderVisible	545ms	739ms	194ms	0.64	26.3%
devManagerIndexVisible	579ms	762ms	183ms	0.52	24%
devStoryVisibleUncached	1.2s	1.4s	195ms	0.56	13.9%
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devAutodocsVisible	512ms	592ms	80ms	0.31	13.5%
devMDXVisible	549ms	629ms	80ms	0.48	12.7%
buildManagerHeaderVisible	475ms	683ms	208ms	0.57	30.5%
buildManagerIndexVisible	505ms	693ms	188ms	0.5	27.1%
buildStoryVisible	506ms	748ms	242ms	0.58	32.4%
buildAutodocsVisible	478ms	697ms	219ms	0.81	31.4%
buildMDXVisible	414ms	609ms	195ms	0.43	32%

Greptile Summary

This pull request improves accessibility for high contrast mode in Storybook's UI components.

• Added visible focus indicators for ActionBar buttons in high contrast mode
• Implemented transparent border for Input components when focused in forced-colors environments
• Enhanced Boolean toggle control with underline for selected value in high contrast mode
• These changes address issue [Bug]: Visual focus indicators (VFIs) aren't visible in high contrast mode #25935, improving keyboard navigation for users with visual impairments

[greptile-apps]

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[MichaelArestad]

I just has one suggestion for slightly tidier code. I very much appreciate you taking the time to add these enhancements for high contrast mode. Thank you!

[MichaelArestad]

If I remember correctly, you can nest media queries in the above selector (below line 94) which should result in not needing to duplicate a complex selector like this one. It's just slightly tidier.

[natainakata]

Media queries are now nested.
Applied to other changes as well.

[Sidnioulz]

@natainakata thanks for your contribution! I've reopened this branch on the Storybook repo to rebase it and check the state of the CI. I'm closing this PR as a result, and I'll make sure the rebase PR gets merged.

You can follow up on #29239.