# Tailwind Design System: Advanced Patterns

Advanced Tailwind CSS v4 patterns including animations, dark mode theming, custom utilities, theme modifiers, namespace overrides, and the v3-to-v4 migration checklist.

## Pattern 5: Native CSS Animations (v4)

```css
/* In your CSS file - native @starting-style for entry animations */
@theme {
  --animate-dialog-in: dialog-fade-in 0.2s ease-out;
  --animate-dialog-out: dialog-fade-out 0.15s ease-in;
}

@keyframes dialog-fade-in {
  from {
    opacity: 0;
    transform: scale(0.95) translateY(-0.5rem);
  }
  to {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
}

@keyframes dialog-fade-out {
  from {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
  to {
    opacity: 0;
    transform: scale(0.95) translateY(-0.5rem);
  }
}

/* Native popover animations using @starting-style */
[popover] {
  transition:
    opacity 0.2s,
    transform 0.2s,
    display 0.2s allow-discrete;
  opacity: 0;
  transform: scale(0.95);
}

[popover]:popover-open {
  opacity: 1;
  transform: scale(1);
}

@starting-style {
  [popover]:popover-open {
    opacity: 0;
    transform: scale(0.95);
  }
}
```

```typescript
// components/ui/dialog.tsx - Using native popover API
import * as DialogPrimitive from '@radix-ui/react-dialog'
import { cn } from '@/lib/utils'

const DialogPortal = DialogPrimitive.Portal

export function DialogOverlay({
  className,
  ref,
  ...props
}: React.ComponentPropsWithoutRef<typeof DialogPrimitive.Overlay> & {
  ref?: React.Ref<HTMLDivElement>
}) {
  return (
    <DialogPrimitive.Overlay
      ref={ref}
      className={cn(
        'fixed inset-0 z-50 bg-black/80',
        'data-[state=open]:animate-fade-in data-[state=closed]:animate-fade-out',
        className
      )}
      {...props}
    />
  )
}

export function DialogContent({
  className,
  children,
  ref,
  ...props
}: React.ComponentPropsWithoutRef<typeof DialogPrimitive.Content> & {
  ref?: React.Ref<HTMLDivElement>
}) {
  return (
    <DialogPortal>
      <DialogOverlay />
      <DialogPrimitive.Content
        ref={ref}
        className={cn(
          'fixed left-1/2 top-1/2 z-50 grid w-full max-w-lg -translate-x-1/2 -translate-y-1/2 gap-4 border border-border bg-background p-6 shadow-lg sm:rounded-lg',
          'data-[state=open]:animate-dialog-in data-[state=closed]:animate-dialog-out',
          className
        )}
        {...props}
      >
        {children}
      </DialogPrimitive.Content>
    </DialogPortal>
  )
}
```

## Pattern 6: Dark Mode with CSS (v4)

```typescript
// providers/ThemeProvider.tsx - Simplified for v4
'use client'

import { createContext, useContext, useEffect, useState } from 'react'

type Theme = 'dark' | 'light' | 'system'

interface ThemeContextType {
  theme: Theme
  setTheme: (theme: Theme) => void
  resolvedTheme: 'dark' | 'light'
}

const ThemeContext = createContext<ThemeContextType | undefined>(undefined)

export function ThemeProvider({
  children,
  defaultTheme = 'system',
  storageKey = 'theme',
}: {
  children: React.ReactNode
  defaultTheme?: Theme
  storageKey?: string
}) {
  const [theme, setTheme] = useState<Theme>(defaultTheme)
  const [resolvedTheme, setResolvedTheme] = useState<'dark' | 'light'>('light')

  useEffect(() => {
    const stored = localStorage.getItem(storageKey) as Theme | null
    if (stored) setTheme(stored)
  }, [storageKey])

  useEffect(() => {
    const root = document.documentElement
    root.classList.remove('light', 'dark')

    const resolved = theme === 'system'
      ? (window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light')
      : theme

    root.classList.add(resolved)
    setResolvedTheme(resolved)

    // Update meta theme-color for mobile browsers
    const metaThemeColor = document.querySelector('meta[name="theme-color"]')
    if (metaThemeColor) {
      metaThemeColor.setAttribute('content', resolved === 'dark' ? '#09090b' : '#ffffff')
    }
  }, [theme])

  return (
    <ThemeContext.Provider value={{
      theme,
      setTheme: (newTheme) => {
        localStorage.setItem(storageKey, newTheme)
        setTheme(newTheme)
      },
      resolvedTheme,
    }}>
      {children}
    </ThemeContext.Provider>
  )
}

export const useTheme = () => {
  const context = useContext(ThemeContext)
  if (!context) throw new Error('useTheme must be used within ThemeProvider')
  return context
}

// components/ThemeToggle.tsx
import { Moon, Sun } from 'lucide-react'
import { useTheme } from '@/providers/ThemeProvider'

export function ThemeToggle() {
  const { resolvedTheme, setTheme } = useTheme()

  return (
    <Button
      variant="ghost"
      size="icon"
      onClick={() => setTheme(resolvedTheme === 'dark' ? 'light' : 'dark')}
    >
      <Sun className="size-5 rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
      <Moon className="absolute size-5 rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
      <span className="sr-only">Toggle theme</span>
    </Button>
  )
}
```

## Advanced v4 Patterns

### Custom Utilities with `@utility`

Define reusable custom utilities:

```css
/* Custom utility for decorative lines */
@utility line-t {
  @apply relative before:absolute before:top-0 before:-left-[100vw] before:h-px before:w-[200vw] before:bg-gray-950/5 dark:before:bg-white/10;
}

/* Custom utility for text gradients */
@utility text-gradient {
  @apply bg-gradient-to-r from-primary to-accent bg-clip-text text-transparent;
}
```

### Theme Modifiers

```css
/* Use @theme inline when referencing other CSS variables */
@theme inline {
  --font-sans: var(--font-inter), system-ui;
}

/* Use @theme static to always generate CSS variables (even when unused) */
@theme static {
  --color-brand: oklch(65% 0.15 240);
}

/* Import with theme options */
@import "tailwindcss" theme(static);
```

### Namespace Overrides

```css
@theme {
  /* Clear all default colors and define your own */
  --color-*: initial;
  --color-white: #fff;
  --color-black: #000;
  --color-primary: oklch(45% 0.2 260);
  --color-secondary: oklch(65% 0.15 200);

  /* Clear ALL defaults for a minimal setup */
  /* --*: initial; */
}
```

### Semi-transparent Color Variants

```css
@theme {
  /* Use color-mix() for alpha variants */
  --color-primary-50: color-mix(in oklab, var(--color-primary) 5%, transparent);
  --color-primary-100: color-mix(
    in oklab,
    var(--color-primary) 10%,
    transparent
  );
  --color-primary-200: color-mix(
    in oklab,
    var(--color-primary) 20%,
    transparent
  );
}
```

### Container Queries

```css
@theme {
  --container-xs: 20rem;
  --container-sm: 24rem;
  --container-md: 28rem;
  --container-lg: 32rem;
}
```

## v3 to v4 Migration Checklist

- [ ] Replace `tailwind.config.ts` with CSS `@theme` block
- [ ] Change `@tailwind base/components/utilities` to `@import "tailwindcss"`
- [ ] Move color definitions to `@theme { --color-*: value }`
- [ ] Replace `darkMode: "class"` with `@custom-variant dark`
- [ ] Move `@keyframes` inside `@theme` blocks (ensures keyframes output with theme)
- [ ] Replace `require("tailwindcss-animate")` with native CSS animations
- [ ] Update `h-10 w-10` to `size-10` (new utility)
- [ ] Remove `forwardRef` (React 19 passes ref as prop)
- [ ] Consider OKLCH colors for better color perception
- [ ] Replace custom plugins with `@utility` directives

## Best Practices

### Do's

- **Use `@theme` blocks** - CSS-first configuration is v4's core pattern
- **Use OKLCH colors** - Better perceptual uniformity than HSL
- **Compose with CVA** - Type-safe variants
- **Use semantic tokens** - `bg-primary` not `bg-blue-500`
- **Use `size-*`** - New shorthand for `w-* h-*`
- **Add accessibility** - ARIA attributes, focus states

### Don'ts

- **Don't use `tailwind.config.ts`** - Use CSS `@theme` instead
- **Don't use `@tailwind` directives** - Use `@import "tailwindcss"`
- **Don't use `forwardRef`** - React 19 passes ref as prop
- **Don't use arbitrary values** - Extend `@theme` instead
- **Don't hardcode colors** - Use semantic tokens
- **Don't forget dark mode** - Test both themes
