feat: use of tailwind v4 apis

[gabrielmfern]

Summary by cubic

Switches the Tailwind integration to v4’s runtime compile API to generate CSS from classes at runtime. This removes our v3 internals, improves CSS variable resolution across layers/media, and adds support for async React components during inlining.

• New Features

  • Added generateRootForClasses powered by tailwindcss compile(), with embedded theme, preflight, and utilities.
  • Made Tailwind component and mapReactTree async to support async function components.
  • Resolved CSS variables across layers and media queries; improved handling of non-inlinable classes.

• Refactors

  • Removed setup-tailwind* and all Tailwind v3 internal imports.
  • Switched build to tsup and set moduleResolution to bundler.
  • Upgraded tailwindcss to 4.1.12 and updated tests/snapshots.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 18e4c8c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Preview	Comments	Updated (UTC)
react-email	Ready	Preview	Comment	Sep 5, 2025 2:10pm
react-email-demo	Error			Sep 5, 2025 2:10pm

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/resend/react-email/@react-email/tailwind@2425

commit: 18e4c8c