Remove Box usage and sx prop from PageLayout

[mperrotti]

Relates to https://github.com/github/primer/issues/5424 and https://github.com/github/primer/issues/5425
Closes https://github.com/github/primer/issues/5796

Changelog

New

Changed

sx prop was removed from PageLayout and its subcomponents

Removed

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 52adc31

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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[Copilot]

Pull Request Overview

This PR removes Box component usage and the sx prop from PageLayout components in Primer React, migrating from styled-components to CSS Modules. The changes support the broader migration from the styled-system approach to a more modern CSS-based implementation.

• Replaces BoxWithFallback components with native HTML elements (div, header, footer)
• Removes sx prop from all PageLayout component interfaces and implementations
• Adds new styled-react wrapper for backward compatibility during the migration period

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/styled-react/src/sx.ts	New utility for handling sx prop in styled-react package
packages/styled-react/src/index.tsx	Adds PageLayout export and removes it from main exports
packages/styled-react/src/components/PageLayout.tsx	New styled-react wrapper providing sx prop compatibility
packages/react/src/PageLayout/PageLayout.tsx	Removes Box usage, sx prop, and migrates to native HTML elements
packages/react/src/PageLayout/PageLayout.stories.tsx	Removes sx prop from story args
packages/react/src/PageLayout/PageLayout.module.css	Adds CSS classes for draggable handle styling
packages/react/src/PageLayout/PageLayout.dev.stories.tsx	Replaces sx prop usage with CSS classes
packages/react/src/PageLayout/PageLayout.dev.stories.module.css	New CSS classes for development story styling

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/3156

[primer-integration]

🟢 ci completed with status success.

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!