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]

Walkthrough

This pull request updates the CSS property namespace mapping in the apply-config-to-theme module. The OLD_TO_NEW_NAMESPACE mapping is modified so that the maxWidth theme key now resolves to the max-width CSS property namespace instead of the container namespace. A corresponding test expectation is updated to reflect this mapping change, ensuring the test validates the new behavior.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: fixing the maxWidth namespace mapping from container to max-width in the v4 migration compatibility layer.
Description check	✅ Passed	The description clearly explains the issue (maxWidth incorrectly mapped to --container namespace), the fix (mapping to max-width), and provides test verification details.
Linked Issues check	✅ Passed	The PR directly addresses #19555 by fixing the OLD_TO_NEW_NAMESPACE mapping to correctly map maxWidth to max-width, preventing conflicts with container query variables and preserving utility semantics.
Out of Scope Changes check	✅ Passed	All changes are scoped to the maxWidth namespace mapping fix in the compatibility layer; no extraneous modifications outside the stated objective are present.

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

---

No actionable comments were generated in the recent review. 🎉

---

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.}