feat(preview-server): update to tailwindcss@v4

[gabrielmfern]

This is exclusive to the UI, so no changes to any components or anything related to user code.

The process for this was to first run the migration script

npx @tailwindcss/upgrade

And then, started migrating the remaining things we had in the JS config to the globals.css file. I also followed the instructions in https://tailwindcss.com/docs/upgrade-guide#buttons-use-the-default-cursor to maintain the pointer cursor for all button-like elements.

---

Summary by cubic

Upgrade preview-server UI to Tailwind CSS v4. Migrates theme and utilities into CSS, updates classes, and preserves v3 visuals (button cursor, border color).

• Refactors

  • Removed tailwind.config.ts; defined theme, keyframes, and arrow-hide via @theme/@Utility in globals.css.
  • Updated class names for v4 (e.g., bg-linear-to-*, w-dvw/h-dvh, outline-hidden, rounded-sm/xs, grow/shrink) and adjusted aria selectors.
  • Added base-layer compatibility (default border-color) and pointer cursor for buttons per upgrade guide.
  • Stopped importing Tailwind config in code; use TailwindConfig from @react-email/tailwind.
  • Enabled Tailwind directives parsing in Biome (css.tailwindDirectives).

• Dependencies

  • Bumped tailwindcss to 4.1.17.
  • Added @tailwindcss/postcss and updated postcss.config; removed autoprefixer.
  • Updated lockfile to reflect new Tailwind v4 toolchain.

^{Written for commit 3740910. Summary will update automatically on new commits.}

[changeset-bot]

🦋 Changeset detected

Latest commit: 3740910

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

This PR includes changesets to release 2 packages

Name	Type
@react-email/preview-server	Patch
react-email	Patch

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[vercel]

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

Project	Deployment	Preview	Comments	Updated (UTC)
react-email	Ready	Preview	Comment	Dec 8, 2025 3:22pm
react-email-demo	Ready	Preview	Comment	Dec 8, 2025 3:22pm

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​tailwindcss/​postcss@​4.1.17

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[pkg-pr-new]

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npm i https://pkg.pr.new/resend/react-email/@react-email/preview-server@2720

commit: 3740910

[cubic-dev-ai]

No issues found across 23 files