[mkantautas]

Summary

@tailwindcss/vite only hands a stylesheet to Tailwind when it uses @apply, @plugin/@config, theme(…), @tailwind utilities or @variant. A stylesheet that only uses @theme is returned as-is:

/* src/theme.css, linked from index.html */
@theme {
  --color-brand: red;
}

.brand {
  color: var(--color-brand);
}

vite build emits this file unchanged, so the browser gets the raw @theme block and --color-brand is never defined. Compiling the same CSS with tailwindcss directly (or with @tailwindcss/postcss) gives :root, :host { --color-brand: red; } and the .brand rule.

Features.AtTheme was added in #18979 for this case, but the Vite plugin's check wasn't updated. This adds Features.AtTheme to it.

Test plan

• Added production build with a stylesheet that only uses @theme to integrations/vite/index.test.ts. On main it fails because the CSS still contains the @theme { … } block; with this change the output has the :root, :host declaration and the .brand rule.
• pnpm vitest --root=./integrations run vite/index.test.ts -t 'only uses|production build|demote': 4 passed.
• prettier --check on the changed files.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: b08e7a6d-fd49-4817-87da-f950da407f35

📥 Commits

Reviewing files that changed from the base of the PR and between 8cc0551 and 6986fb2.

📒 Files selected for processing: 3

• CHANGELOG.md
• integrations/vite/index.test.ts
• packages/@tailwindcss-vite/src/index.ts

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 7 remain after this review.

Walkthrough

Root.generate now continues CSS generation when the compiler feature mask includes Features.AtTheme. A Vite production-build test checks that a theme-only stylesheet produces the expected custom property and preserves its variable reference. The changelog records the change.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 6986f

The change is ready to merge after normal checks; no actionable issue was identified.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: processing stylesheets that use only @theme in @tailwindcss/vite.
Description check		The description is directly related to the changeset. It explains the @theme processing issue, the code change, and the added integration test.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[greptile-apps]

Confidence Score: 5/5

[Medium impact] This PR appears safe to merge.

_{Reviews (1) · Last reviewed commit: "Add changelog entry for #20599" · Reviewed by Greptile}