UI: Ensure preview error displays use a readable text color

[Sidnioulz]

Closes #32749

What I did

Sets CSS selectors with high specificty on all nodes of both Preview Error displays:

• "No preview" which triggers when there are no stories
• The error wrapper that shows a title, message and stack trace

This PR may have side effects on existing users' CSS customisations to the aforementioned UIs. We need to decide if we consider that a potential breaking change.

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

1. Visit http://localhost:6006/?path=/story/preview-errors--my-error-with-custom-css
2. Visit http://localhost:6006/?path=/story/preview-errors--missing-with-custom-css

Documentation

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• 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.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

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

Summary by CodeRabbit

• Style

  • Improved error display visual styling with updated colors and enhanced readability
  • Refined preview block spacing and formatting consistency

• Tests

  • Added new error display story variants with custom styling scenarios

_{✏️ Tip: You can customize this high-level summary in your review settings.}

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View your CI Pipeline Execution ↗ for commit dea343c

Command	Status	Duration	Result
nx run-many -t compile,check,knip,test,pretty-d...	✅ Succeeded	11m 10s	View ↗

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☁️ Nx Cloud last updated this comment at 2026-01-19 16:22:43 UTC

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 0c924be

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☁️ Nx Cloud last updated this comment at 2026-01-19 12:35:53 UTC

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 0c924be

Command	Status	Duration	Result
nx run-many -t compile,check,knip,test,pretty-d...	⏳ In Progress	...	View ↗

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☁️ Nx Cloud last updated this comment at 2026-01-19 12:47:17 UTC

[coderabbitai]

📝 Walkthrough

Walkthrough

Updates CSS selectors and visual styling in the base preview HTML file to refine error display formatting and color schemes. Introduces two new story variants in the error stories file to demonstrate custom CSS styling application.

Changes

Cohort / File(s)	Summary
Preview HTML Styling code/core/assets/server/base-preview-head.html	CSS selector formatting normalization (removed spaces around combinators); visual theme adjustments for error/nopreview blocks (background color rgb(247,247,247), explicit text colors); new .sb-errordisplay_main and .sb-errordisplay_code blocks with layout, borders, and monospace typography; universal color resets for readability.
Story Variants code/core/src/preview-api/Errors.stories.tsx	Added internal StyleDecorator utility; introduced two new story exports (MyErrorWithCustomCSS, MissingWithCustomCSS) that extend existing stories with custom CSS styling via decorators.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

✨ Finishing touches

• 📝 Generate docstrings

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[storybook-app-bot]

Package Benchmarks

^{Commit: dea343c, ran on 19 January 2026 at 16:21:57 UTC}

The following packages have significant changes to their size or dependencies:

storybook

	Before	After	Difference
Dependency count	49	49	0
Self size	20.30 MB	20.31 MB	🚨 +10 KB 🚨
Dependency size	16.52 MB	16.52 MB	🎉 -4 B 🎉
Bundle Size Analyzer	Link	Link

@storybook/react-native-web-vite

	Before	After	Difference
Dependency count	159	159	0
Self size	30 KB	30 KB	🚨 +8 B 🚨
Dependency size	23.00 MB	23.12 MB	🚨 +115 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	183	183	0
Self size	775 KB	775 KB	🚨 +139 B 🚨
Dependency size	67.38 MB	67.46 MB	🚨 +80 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	176	176	0
Self size	30 KB	30 KB	🎉 -4 B 🎉
Dependency size	65.95 MB	66.03 MB	🚨 +80 KB 🚨
Bundle Size Analyzer	Link	Link

create-storybook

	Before	After	Difference
Dependency count	50	50	0
Self size	1000 KB	999 KB	🎉 -48 B 🎉
Dependency size	36.82 MB	36.83 MB	🚨 +10 KB 🚨
Bundle Size Analyzer	node	node