fix(compat): map maxWidth to max-width namespace in v4 migration

[NssGourav]

Summary

In Tailwind CSS v4, the migration logic for v3 configurations incorrectly maps the maxWidth theme key to the
--container-* CSS variable namespace. This causes clashes with container query variables and breaks the primary max-w-* utility design.

This PR updates OLD_TO_NEW_NAMESPACE to correctly map maxWidth to max-width.

Fixes #19555

Test Plan

Verified by updating existing core compatibility tests.

Execution command:

pnpm vitest packages/tailwindcss/src/compat/apply-config-to-theme.test.ts --run

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: aed966e7-ae88-4656-be26-0d617e755435

📥 Commits

Reviewing files that changed from the base of the PR and between 2670a42 and f43279c.

📒 Files selected for processing (1)

• packages/tailwindcss/src/compat/apply-config-to-theme.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/tailwindcss/src/compat/apply-config-to-theme.ts

---

Walkthrough

The pull request changes the CSS property namespace mapping in apply-config-to-theme: the OLD_TO_NEW_NAMESPACE mapping now maps the maxWidth theme key to the max-width namespace instead of container. A test in apply-config-to-theme.test.ts is updated to expect the resolved value from the --max-width CSS property variable for the 9xs key.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main fix: mapping maxWidth to the max-width namespace in v4 migration, which aligns with the primary changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining the bug (incorrect mapping to container namespace), the fix (mapping to max-width), and providing test verification details.
Linked Issues check	✅ Passed	The PR successfully addresses issue #19555 by mapping maxWidth to the max-width namespace instead of container, preventing clashes with container query variables and preserving intended semantics after v3-to-v4 migration.
Out of Scope Changes check	✅ Passed	All changes are scoped to the maxWidth namespace mapping fix: updates to OLD_TO_NEW_NAMESPACE and corresponding test expectation, with no unrelated modifications.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Tip

CodeRabbit can use TruffleHog to scan for secrets in your code with verification capabilities.

Add a TruffleHog config file (e.g. trufflehog-config.yml, trufflehog.yml) to your project to customize detectors and scanning behavior. The tool runs only when a config file is present.

[NssGourav]

@RobinMalfait can you please review this pr and let me know anything to change