Tailwind V4 Shadcn

# Advanced Usage Patterns

**Purpose**: Advanced customization and component patterns for experienced Tailwind v4 + shadcn/ui developers
**When to Load**: User asks for custom colors beyond defaults, advanced component patterns, composition best practices, or component customization

---

## Custom Colors

Add new semantic colors beyond the default palette:

```css
:root {
  --brand: hsl(280 65% 60%);
  --brand-foreground: hsl(0 0% 100%);
}

.dark {
  --brand: hsl(280 75% 70%);
  --brand-foreground: hsl(280 20% 10%);
}

@theme inline {
  --color-brand: var(--brand);
  --color-brand-foreground: var(--brand-foreground);
}
```

**Usage:**
```tsx
<div className="bg-brand text-brand-foreground">Branded Component</div>
```

**Key Pattern**: Define CSS variable in `:root`/`.dark`, then reference in `@theme inline` with `--color-` prefix.

---

## Migration from Tailwind v3

For complete v3 → v4 migration steps, see `references/migration-guide.md`.

**Quick Summary**:
- Remove `tailwind.config.js` (v4 uses CSS configuration)
- Convert hardcoded colors to CSS variables
- Update plugin syntax: `require('tailwindcss/plugin')(plugin)` in v3 config → `@plugin "plugin-name"` in CSS
- Change Vite plugin: `require('tailwindcss')` or `import tailwindcss from 'tailwindcss'` in v3 → `import tailwindcss from '@tailwindcss/vite'` in v4

---

## Component Best Practices

### 1. Always Use Semantic Tokens

**✅ CORRECT:**
```tsx
<Button variant="destructive">Delete</Button>
```

**❌ WRONG:**
```tsx
<Button className="bg-red-600">Delete</Button>
```

**Why**: Semantic tokens (`destructive`, `primary`, `secondary`) adapt to theme changes. Hardcoded colors break dark mode and theme customization.

---

### 2. Use `cn()` for Conditional Styling

**Import:**
```tsx
import { cn } from "@/lib/utils"
```

**Usage:**
```tsx
<div className={cn(
  "base-class",
  isActive && "active-class",
  hasError && "error-class"
)} />
```

**What `cn()` does**: Merges Tailwind classes intelligently (later classes override earlier ones).

---

### 3. Compose shadcn/ui Components

**Pattern:**
```tsx
<Dialog>
  <DialogTrigger asChild>
    <Button>Open</Button>
  </DialogTrigger>
  <DialogContent>
    <DialogHeader>
      <DialogTitle>Title</DialogTitle>
    </DialogHeader>
  </DialogContent>
</Dialog>
```

**Key Concept**: Use composition (wrapping components) rather than customization (passing props).

---

## Advanced Patterns

### Conditional Theme Variables

Apply different variables based on state:

```tsx
<div className={cn(
  "rounded-lg p-4",
  variant === "success" && "bg-success text-success-foreground",
  variant === "error" && "bg-destructive text-destructive-foreground"
)} />
```

### Custom Radius Tokens

Add semantic border radius:

```css
@theme inline {
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 1rem;
}
```

Usage: `className="rounded-[var(--radius-lg)]"`

### Component Variants Pattern

Use `cva()` from `class-variance-authority` for complex variants:

```tsx
import { cva } from "class-variance-authority"

const buttonVariants = cva(
  "inline-flex items-center justify-center rounded-md",
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground",
        destructive: "bg-destructive text-destructive-foreground",
      },
      size: {
        default: "h-10 px-4 py-2",
        sm: "h-9 px-3",
        lg: "h-11 px-8",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "default",
    },
  }
)
```

---

## Official Resources

- Tailwind v4 Docs: https://tailwindcss.com/blog/tailwindcss-v4-beta
- shadcn/ui: https://ui.shadcn.com
- class-variance-authority: https://cva.style/docs


# Common Gotchas & Solutions

## Critical Failures (Will Break Your Build)

### 1. `:root` Inside `@layer base`

❌ **WRONG:**
```css
@layer base {
  :root {
    --background: hsl(0 0% 100%);
  }
}
```

✅ **CORRECT:**
```css
:root {
  --background: hsl(0 0% 100%);
}

@layer base {
  body {
    background-col