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name: styling-nativewind-v4-expo description: >- Sets up and uses NativeWind v4 (Tailwind CSS v3) in Expo React Native apps, including Expo Router. Configures tailwind.config.js, global.css, babel.config.js (jsxImportSource + nativewind/babel), metro.config.js (withNativeWind + input), and app.json (web bundler metro). Troubleshoots “className not applying”, Tailwind CLI compilation, and Metro cache issues. Implements reusable components/variants, dark mode + theming via CSS variables (vars/useColorScheme), and third-party component styling (remapProps/cssInterop). Use when working on Expo projects using NativeWind v4, Tailwind-style className utilities, or when debugging NativeWind configuration.

NativeWind v4 for Expo (React Native)

Non‑negotiables (v4)

• Use Tailwind CSS v3 and include presets: [require("nativewind/preset")] in tailwind.config.js.
• Keep exactly one Tailwind entry CSS file (commonly global.css) and keep its path consistent across:
  • metro.config.js → withNativeWind(..., { input: "./global.css" })
  • your app entry → import "./global.css" (or import "../global.css" from app/_layout.tsx)
• Keep nativewind/babel in Babel presets and set jsxImportSource: "nativewind" on babel-preset-expo.
• After any config change, restart Metro without cache: npx expo start --clear.

Quick start checklist

Copy/paste and tick off:

• Install deps (NativeWind + Tailwind + peers). See references/expo-setup.md.
• Create/verify tailwind.config.js (content globs + nativewind/preset).
• Create/verify global.css with Tailwind directives.
• Create/verify babel.config.js (jsxImportSource + nativewind/babel).
• Create/verify metro.config.js (wrap config with withNativeWind, set input).
• If targeting web, set app.json → expo.web.bundler = "metro".
• If TypeScript, add nativewind-env.d.ts with /// <reference types="nativewind/types" />.
• Start with cache cleared and validate on-device + web: npx expo start --clear.
• Validate with an obvious “smoke test” screen: background colour + centred text.

Project type selection

• Expo Router: entry is usually app/_layout.tsx → import CSS there (relative path is typically ../global.css).
• Classic: entry is usually App.tsx → import CSS there (./global.css).

If unsure, search package.json for "main": "expo-router/entry".

Implementation patterns

Build reusable components (recommended)

Accept className, merge defaults, and optionally use a class-variance helper.

Read: references/patterns.md

Style third‑party components (only when necessary)

Use remapProps (multiple style props) or cssInterop (map a class prop to a style prop).

Read: references/third-party-components.md

Dark mode + theming

Use useColorScheme / colorScheme.set() and CSS variables via vars().

Read: references/theming-dark-mode.md

Safe area utilities

On Expo Router, do not add your own SafeAreaProvider (Router already does). Use p-safe, pt-safe, etc.

If you are not using Expo Router, wrap the root with SafeAreaProvider.

Troubleshooting workflow (always in this order)

1. Start Expo without cache: npx expo start --clear.
2. Verify Tailwind CLI works by compiling your CSS entry file to an output file.
3. Confirm the “three paths” match:
   • CSS file exists
   • metro.config.js input points to it
   • your app imports it from the entry component
4. Confirm tailwind.config.js content globs include every directory that contains className strings.
5. Only then debug platform-specific behaviour (web bundler, Router, safe area, etc).

Read: references/troubleshooting.md

THE EXACT PROMPT — NativeWind v4 config audit

Use this prompt to perform a deterministic audit of an existing repo:

You are auditing an Expo React Native repo for NativeWind v4 correctness.

1) Identify whether the project uses Expo Router (app/ directory + package.json main = expo-router/entry) or classic App.tsx.
2) Check and report on:
   - tailwind.config.js: presets + content globs
   - global.css: Tailwind directives exist
   - babel.config.js: jsxImportSource nativewind + nativewind/babel in presets; preserve any existing required plugins
   - metro.config.js: withNativeWind wrapper; input path matches the CSS file
   - app.json: web bundler metro when web is used
   - TypeScript: nativewind-env.d.ts present and correctly named
3) For every issue, propose the minimal diff needed to fix it.
4) End by listing the exact commands to restart Metro and validate the fix.