tailwind-theme-builder

# Tailwind Theme Builder

Set up a fully themed Tailwind v4 + shadcn/ui project with dark mode. Produces configured CSS, theme provider, and working component library.

## Architecture: The Four-Step Pattern

Tailwind v4 requires a specific architecture for CSS variable-based theming. This pattern is **mandatory** -- skipping or modifying steps breaks the theme.

### How It Works

```
CSS Variable Definition --> @theme inline Mapping --> Tailwind Utility Class
--background           --> --color-background     --> bg-background
(with hsl() wrapper)      (references variable)     (generated class)
```

Dark mode switching:
```
ThemeProvider toggles .dark class on <html>
  --> CSS variables update automatically (.dark overrides :root)
  --> Tailwind utilities reference updated variables
  --> UI updates without re-render
```

### Best Practices

- **Semantic names:** Use `--primary` not `--blue-500`
- **Foreground pairing:** Every background colour needs a foreground (`--primary` + `--primary-foreground`)
- **WCAG contrast:** Normal text 4.5:1, large text 3:1, UI components 3:1
- **Chart colours:** Use separate variables with `@theme inline` mapping, reference via `var(--chart-1)` in style props

---

## Workflow

### Step 1: Install Dependencies

```bash
pnpm add tailwindcss @tailwindcss/vite
pnpm add -D @types/node tw-animate-css
pnpm dlx shadcn@latest init

# Delete v3 config if it exists
rm -f tailwind.config.ts
```

### Step 2: Configure Vite

Copy `assets/vite.config.ts` or add the Tailwind plugin:

```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') } }
})
```

### Step 3: Four-Step CSS Architecture (Mandatory)

This exact order is required. Skipping steps breaks the theme.

**src/index.css:**

```css
@import "tailwindcss";
@import "tw-animate-css";

/* 1. Define CSS variables at root (NOT inside @layer base) */
:root {
  --background: hsl(0 0% 100%);
  --foreground: hsl(222.2 84% 4.9%);
  --primary: hsl(221.2 83.2% 53.3%);
  --primary-foreground: hsl(210 40% 98%);
  /* ... all semantic tokens */
}

.dark {
  --background: hsl(222.2 84% 4.9%);
  --foreground: hsl(210 40% 98%);
  --primary: hsl(217.2 91.2% 59.8%);
  --primary-foreground: hsl(222.2 47.4% 11.2%);
}

/* 2. Map variables to Tailwind utilities */
@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
  --color-primary: var(--primary);
  --color-primary-foreground: var(--primary-foreground);
}

/* 3. Apply base styles (NO hsl() wrapper here) */
@layer base {
  body {
    background-color: var(--background);
    color: var(--foreground);
  }
}
```

**Result:** `bg-background`, `text-primary` etc. work automatically. Dark mode switches via `.dark` class -- no `dark:` variants needed for semantic colours.

### Step 4: Set Up Dark Mode

Copy `assets/theme-provider.tsx` to your components directory, then wrap your app:

```typescript
import { ThemeProvider } from '@/components/theme-provider'

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

Add a theme toggle -- install the dropdown menu then use the ModeToggle component below:

```bash
pnpm dlx shadcn@latest add dropdown-menu
```

```typescript
// src/components/mode-toggle.tsx
import { Moon, Sun } from "lucide-react"
import { Button } from "@/components/ui/button"
import {
  DropdownMenu,
  DropdownMenuContent,
  DropdownMenuItem,
  DropdownMenuTrigger,
} from "@/components/ui/dropdown-menu"
import { useTheme } from "@/components/theme-provider"

export function ModeToggle() {
  const { setTheme } = useTheme()

  return (
    <DropdownMenu>
      <DropdownMenuTrigger asChild>
        <Button variant="outline" size="icon">
          <Sun className="h-[1.2rem] w-[1.2rem] rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
          <Moon className="absolute h-[1.2rem] w-[1.2rem] rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
          <span className="sr-only">Toggle theme</span>
        </Button>
      </DropdownMenuTrigger>
      <DropdownMenuContent align="end">
        <DropdownMenuItem onClick={() => setTheme("light")}>Light</DropdownMenuItem>
        <DropdownMenuItem onClick={() => setTheme("dark")}>Dark</DropdownMenuItem>
        <DropdownMenuItem onClick={() => setTheme("system")}>System</DropdownMenuItem>
      </DropdownMenuContent>
    </DropdownMenu>
  )
}
```

### Step 5: Configure components.json

```json
{
  "tailwind": {
    "config": "",
    "css": "src/index.css",
    "baseColor": "slate",
    "cssVariables": true
  }
}
```

`"config": ""` is critical -- v4 doesn't use tailwind.config.ts.

---

## Critical Rules

**Always:**
- Wrap colours with `hsl()` in `:root`/`.dark`
- Use `@theme inline` to map all CSS variables
- Use `@tailwindcss/vite` plugin (NOT PostCSS)
- Delete `tailwind.config.ts` if it exists

**Never:**
- Put `:root`/`.dark` inside `@layer base`
- Use `.dark { @theme { } }` (v4 doesn't support nested @theme)
- Double-wrap: `hsl(var(--background))`
- Use `@apply` with `@layer base` classes (use `@utility` instead)

---

## All 18 Gotchas

### Quick Diagnosis

| # | Symptom | Cause | Fix |
|---|---------|-------|-----|
| 1 | Variables ignored / theme broken | `:root` inside `@layer base` | Move `:root` and `.dark` to root level |
| 2 | Dark mode colours not switching | `.dark { @theme { } }` | Use CSS variables + single `@theme inline` |
| 3 | Colours all black/white | Double `hsl()` wrapping | Use `var(--background)` not `hsl(var(...))` |
| 4 | `bg-primary` not generated | Colours in `tailwind.config.ts` | Delete config, use `@theme inline` |
| 5 | `bg-background` class missing | No `@theme inline` block | Add `@theme inline`