tailwind-v4-shadcn

What this skill does

# Tailwind v4 + shadcn/ui Production Stack

**Production-tested**: WordPress Auditor (https://wordpress-auditor.webfonts.workers.dev)
**Last Updated**: 2026-01-20
**Versions**: [email protected], @tailwindcss/[email protected]
**Status**: Production Ready ✅

---

## Quick Start (Follow This Exact Order)

```bash
# 1. Install dependencies
pnpm add tailwindcss @tailwindcss/vite
pnpm add -D @types/node tw-animate-css
pnpm dlx shadcn@latest init

# 2. Delete v3 config if exists
rm tailwind.config.ts  # v4 doesn't use this file
```

**vite.config.ts**:
```typescript
import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'
import tailwindcss from '@tailwindcss/vite'
import path from 'path'

export default defineConfig({
  plugins: [react(), tailwindcss()],
  resolve: { alias: { '@': path.resolve(__dirname, './src') } }
})
```

**components.json** (CRITICAL):
```json
{
  "tailwind": {
    "config": "",              // ← Empty for v4
    "css": "src/index.css",
    "baseColor": "slate",
    "cssVariables": true
  }
}
```

---

## The Four-Step Architecture (MANDATORY)

Skipping steps will break your theme. Follow exactly:

### Step 1: Define CSS Variables at Root

```css
/* src/index.css */
@import "tailwindcss";
@import "tw-animate-css";  /* Required for shadcn/ui animations */

:root {
  --background: hsl(0 0% 100%);      /* ← hsl() wrapper required */
  --foreground: hsl(222.2 84% 4.9%);
  --primary: hsl(221.2 83.2% 53.3%);
  /* ... all light mode colors */
}

.dark {
  --background: hsl(222.2 84% 4.9%);
  --foreground: hsl(210 40% 98%);
  --primary: hsl(217.2 91.2% 59.8%);
  /* ... all dark mode colors */
}
```

**Critical**: Define at root level (NOT inside `@layer base`). Use `hsl()` wrapper.

### Step 2: Map Variables to Tailwind Utilities

```css
@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
  --color-primary: var(--primary);
  /* ... map ALL CSS variables */
}
```

**Why**: Generates utility classes (`bg-background`, `text-primary`). Without this, utilities won't exist.

### Step 3: Apply Base Styles

```css
@layer base {
  body {
    background-color: var(--background);  /* NO hsl() wrapper here */
    color: var(--foreground);
  }
}
```

**Critical**: Reference variables directly. Never double-wrap: `hsl(var(--background))`.

### Step 4: Result - Automatic Dark Mode

```tsx
<div className="bg-background text-foreground">
  {/* No dark: variants needed - theme switches automatically */}
</div>
```

---

## Dark Mode Setup

**1. Create ThemeProvider** (see `templates/theme-provider.tsx`)

**2. Wrap App**:
```typescript
// src/main.tsx
import { ThemeProvider } from '@/components/theme-provider'

ReactDOM.createRoot(document.getElementById('root')!).render(
  <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
    <App />
  </ThemeProvider>
)
```

**3. Add Theme Toggle**:
```bash
pnpm dlx shadcn@latest add dropdown-menu
```

See `reference/dark-mode.md` for ModeToggle component.

---

## Critical Rules

### ✅ Always Do:

1. Wrap colors with `hsl()` in `:root`/`.dark`: `--bg: hsl(0 0% 100%);`
2. Use `@theme inline` to map all CSS variables
3. Set `"tailwind.config": ""` in components.json
4. Delete `tailwind.config.ts` if exists
5. Use `@tailwindcss/vite` plugin (NOT PostCSS)

### ❌ Never Do:

1. Put `:root`/`.dark` inside `@layer base` (causes cascade issues)
2. Use `.dark { @theme { } }` pattern (v4 doesn't support nested @theme)
3. Double-wrap colors: `hsl(var(--background))`
4. Use `tailwind.config.ts` for theme (v4 ignores it)
5. Use `@apply` directive (deprecated in v4, see error #7)
6. Use `dark:` variants for semantic colors (auto-handled)
7. Use `@apply` with `@layer base` or `@layer components` classes (v4 breaking change - use `@utility` instead) | [Source](https://github.com/tailwindlabs/tailwindcss/discussions/17082)
8. Wrap ANY styles in `@layer base` without understanding CSS layer ordering (see error #8) | [Source](https://github.com/tailwindlabs/tailwindcss/discussions/16002)

---

## Common Errors & Solutions

This skill prevents **8 documented errors**.

### 1. ❌ tw-animate-css Import Error

**Error**: "Cannot find module 'tailwindcss-animate'"

**Cause**: shadcn/ui deprecated `tailwindcss-animate` for v4.

**Solution**:
```bash
# ✅ DO
pnpm add -D tw-animate-css

# Add to src/index.css:
@import "tailwindcss";
@import "tw-animate-css";

# ❌ DON'T
npm install tailwindcss-animate  # v3 only
```

---

### 2. ❌ Colors Not Working

**Error**: `bg-primary` doesn't apply styles

**Cause**: Missing `@theme inline` mapping

**Solution**:
```css
@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
  --color-primary: var(--primary);
  /* ... map ALL CSS variables */
}
```

---

### 3. ❌ Dark Mode Not Switching

**Error**: Theme stays light/dark

**Cause**: Missing ThemeProvider

**Solution**:
1. Create ThemeProvider (see `templates/theme-provider.tsx`)
2. Wrap app in `main.tsx`
3. Verify `.dark` class toggles on `<html>` element

---

### 4. ❌ Duplicate @layer base

**Error**: "Duplicate @layer base" in console

**Cause**: shadcn init adds `@layer base` - don't add another

**Solution**:
```css
/* ✅ Correct - single @layer base */
@import "tailwindcss";

:root { --background: hsl(0 0% 100%); }

@theme inline { --color-background: var(--background); }

@layer base { body { background-color: var(--background); } }
```

---

### 5. ❌ Build Fails with tailwind.config.ts

**Error**: "Unexpected config file"

**Cause**: v4 doesn't use `tailwind.config.ts` (v3 legacy)

**Solution**:
```bash
rm tailwind.config.ts
```

v4 configuration happens in `src/index.css` using `@theme` directive.

---

### 6. ❌ @theme inline Breaks Dark Mode in Multi-Theme Setups

**Error**: Dark mode doesn't switch when using `@theme inline` with custom variants (e.g., `data-mode="dark"`)
**Source**: [GitHub Discussion #18560](https://github.com/tailwindlabs/tailwindcss/discussions/18560)

**Cause**: `@theme inline` bakes variable VALUES into utilities at build time. When dark mode changes the underlying CSS variables, utilities don't update because they reference hardcoded values, not variables.

**Why It Happens**:
- `@theme inline` inlines VALUES at build time: `bg-primary` → `background-color: oklch(...)`
- Dark mode overrides change the CSS variables, but utilities already have baked-in values
- The CSS specificity chain breaks

**Solution**: Use `@theme` (without inline) for multi-theme scenarios:

```css
/* ✅ CORRECT - Use @theme without inline */
@custom-variant dark (&:where([data-mode=dark], [data-mode=dark] *));

@theme {
  --color-text-primary: var(--color-slate-900);
  --color-bg-primary: var(--color-white);
}

@layer theme {
  [data-mode="dark"] {
    --color-text-primary: var(--color-white);
    --color-bg-primary: var(--color-slate-900);
  }
}
```

**When to use inline**:
- Single theme + dark mode toggle (like shadcn/ui default) ✅
- Referencing other CSS variables that don't change ✅

**When NOT to use inline**:
- Multi-theme systems (data-theme="blue" | "green" | etc.) ❌
- Dynamic theme switching beyond light/dark ❌

**Maintainer Guidance** (Adam Wathan):
> "It's more idiomatic in v4 for the actual generated CSS to reference your theme variables. I would personally only use inline when things don't work without it."

---

### 7. ❌ @apply with @layer base/components (v4 Breaking Change)

**Error**: `Cannot apply unknown utility class: custom-button`
**Source**: [GitHub Discussion #17082](https://github.com/tailwindlabs/tailwindcss/discussions/17082)

**Cause**: In v3, classes defined in `@layer base` and `@layer components` could be used with `@apply`. In v4, this is a breaking architectural change.

**Why It Happens**: v4 doesn't "hijack" the native CSS `@layer` at-rule anymore. Only classes defined with `@utility` are available to `@apply`.

**Migration**:
```css
/* ❌ v3 pattern (worked) */
@layer components {
  .custom-button {
    @ap