Theming: Set themes.normal according to user preference and export getPreferredColorScheme

[elisezhg]

Closes #28664

What I did

• Set themes.normal to either the light or dark theme, according to the user preference
• Export getPreferredColorScheme as suggested in the issue so it can be used in custom themes

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. Run a sandbox for template, e.g. yarn task --task sandbox --start-from auto --template react-vite/default-ts
2. Set the docs theme to themes.normal in your preview.ts:

const preview: Preview = {
  parameters: {
    controls: {
      matchers: {
        color: /(background|color)$/i,
        date: /Date$/i,
      },
    },
    // ***********************
    docs: {
      theme: themes.normal,
    },
    // ***********************
  },
};

3. Open Storybook in your browser
4. Notice that the docs pages' theme is now in sync with the user preference

Documentation

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

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/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 canary-release-pr.yml --field pr=<PR_NUMBER>

name	before	after	diff	z	%
createSize	0 B	0 B	0 B	-	-
generateSize	77.8 MB	77.8 MB	0 B	1.33	0%
initSize	143 MB	143 MB	579 B	1.19	0%
diffSize	65.6 MB	65.6 MB	579 B	1.18	0%
buildSize	7.19 MB	7.19 MB	431 B	-0.86	0%
buildSbAddonsSize	1.85 MB	1.85 MB	225 B	-0.69	0%
buildSbCommonSize	195 kB	195 kB	0 B	-	0%
buildSbManagerSize	1.87 MB	1.87 MB	192 B	0.45	0%
buildSbPreviewSize	0 B	0 B	0 B	-	-
buildStaticSize	0 B	0 B	0 B	-	-
buildPrebuildSize	3.92 MB	3.92 MB	417 B	-0.68	0%
buildPreviewSize	3.28 MB	3.28 MB	14 B	-0.9	0%
testBuildSize	0 B	0 B	0 B	-	-
testBuildSbAddonsSize	0 B	0 B	0 B	-	-
testBuildSbCommonSize	0 B	0 B	0 B	-	-
testBuildSbManagerSize	0 B	0 B	0 B	-	-
testBuildSbPreviewSize	0 B	0 B	0 B	-	-
testBuildStaticSize	0 B	0 B	0 B	-	-
testBuildPrebuildSize	0 B	0 B	0 B	-	-
testBuildPreviewSize	0 B	0 B	0 B	-	-

name	before	after	diff	z	%
createTime	7.2s	7.1s	-63ms	-0.93	-0.9%
generateTime	21.1s	20.6s	-458ms	-0.18	-2.2%
initTime	14.6s	14.8s	142ms	-0.16	1%
buildTime	11.5s	10.6s	-870ms	1.43	🔰-8.2%
testBuildTime	0ms	0ms	0ms	-	-
devPreviewResponsive	5.5s	5.5s	-13ms	0.2	-0.2%
devManagerResponsive	4.1s	3.7s	-312ms	-0.29	-8.2%
devManagerHeaderVisible	755ms	580ms	-175ms	-0.51	-30.2%
devManagerIndexVisible	799ms	608ms	-191ms	-0.48	-31.4%
devStoryVisibleUncached	2s	1.3s	-716ms	-1.26	🔰-51.8%
devStoryVisible	800ms	609ms	-191ms	-0.54	-31.4%
devAutodocsVisible	711ms	469ms	-242ms	-0.74	-51.6%
devMDXVisible	577ms	494ms	-83ms	-0.62	-16.8%
buildManagerHeaderVisible	595ms	511ms	-84ms	-0.86	-16.4%
buildManagerIndexVisible	682ms	602ms	-80ms	-0.85	-13.3%
buildStoryVisible	575ms	503ms	-72ms	-0.87	-14.3%
buildAutodocsVisible	562ms	409ms	-153ms	-0.84	-37.4%
buildMDXVisible	545ms	409ms	-136ms	-1.08	-33.3%

Greptile Summary

This pull request introduces dynamic theming based on user preferences and exports a utility function for broader use.

• Updated code/core/src/manager/globals/exports.ts: Added getPreferredColorScheme to global exports.
• Modified code/core/src/theming/create.ts: Introduced dynamic setting of themes.normal based on user preference.
• Updated code/core/src/theming/index.ts: Exported getPreferredColorScheme utility function.
• Enhanced code/core/src/theming/tests/create.test.js: Added tests to verify themes.normal respects user preferences.

[greptile-apps]

LGTM

_{4 file(s) reviewed, no comment(s)
Edit PR Review Bot Settings}

[nx-cloud]

☁️ Nx Cloud Report

CI is running/has finished running commands for commit 79ad963. As they complete they will appear below. Click to see the status, the terminal output, and the build insights.

📂 See all runs for this CI Pipeline Execution

---

✅ Successfully ran 1 target

• nx run-many -t build --parallel=3

---

Sent with 💌 from NxCloud.

[ndelangen]

@cdedreuille are you ok with this?

[thomasaull]

I just found this, when I was setting a brandImage like this:

import { addons } from '@storybook/manager-api'
import { themes } from '@storybook/theming'

addons.setConfig({
  theme: {
    ...themes.normal,
    brandImage: 'path/to/my/logo.svg',
  },
})

and the dark mode following the system preferences would not work anymore.

The development of the MR seems to be finished but it was not merged yet, is there anything which needs to be done still?

@ndelangen Looks like @cdedreuille didn’t find the time to review this, is there anyone else who could bring this forward?