# shadcn/ui - Customization

## Theming with CSS Variables

shadcn/ui uses CSS variables for theming. Customize in `globals.css`:

```css
@layer base {
  :root {
    --background: 0 0% 100%;
    --foreground: 222.2 84% 4.9%;
    --primary: 222.2 47.4% 11.2%;
    --primary-foreground: 210 40% 98%;
    --secondary: 210 40% 96.1%;
    --secondary-foreground: 222.2 47.4% 11.2%;
    --muted: 210 40% 96.1%;
    --muted-foreground: 215.4 16.3% 46.9%;
    --accent: 210 40% 96.1%;
    --accent-foreground: 222.2 47.4% 11.2%;
    --destructive: 0 84.2% 60.2%;
    --destructive-foreground: 210 40% 98%;
    --border: 214.3 31.8% 91.4%;
    --input: 214.3 31.8% 91.4%;
    --ring: 222.2 84% 4.9%;
    --radius: 0.5rem;
  }

  .dark {
    --background: 222.2 84% 4.9%;
    --foreground: 210 40% 98%;
    --primary: 210 40% 98%;
    --primary-foreground: 222.2 47.4% 11.2%;
    /* ... other dark mode variables */
  }
}
```

## Adding Custom Variants to Button

Since you own the code, extend components directly:

```tsx
// components/ui/button.tsx
import * as React from "react"
import { Slot } from "@radix-ui/react-slot"
import { cva, type VariantProps } from "class-variance-authority"
import { cn } from "@/lib/utils"

const buttonVariants = cva(
  "inline-flex items-center justify-center rounded-md text-sm font-medium transition-colors",
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground hover:bg-primary/90",
        destructive: "bg-destructive text-destructive-foreground hover:bg-destructive/90",
        outline: "border border-input bg-background hover:bg-accent",
        // Add custom variant
        custom: "bg-gradient-to-r from-purple-500 to-pink-500 text-white",
      },
      size: {
        default: "h-10 px-4 py-2",
        sm: "h-9 rounded-md px-3",
        lg: "h-11 rounded-md px-8",
        // Add custom size
        xl: "h-14 rounded-md px-10 text-lg",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "default",
    },
  }
)

export interface ButtonProps
  extends React.ButtonHTMLAttributes<HTMLButtonElement>,
    VariantProps<typeof buttonVariants> {
  asChild?: boolean
}

const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
  ({ className, variant, size, asChild = false, ...props }, ref) => {
    const Comp = asChild ? Slot : "button"
    return (
      <Comp className={cn(buttonVariants({ variant, size, className }))} ref={ref} {...props} />
    )
  }
)
Button.displayName = "Button"

export { Button, buttonVariants }
```

## Custom Color Themes

To use a custom brand color as primary:

```css
@layer base {
  :root {
    /* Custom brand color (blue) */
    --primary: 217 91% 60%;
    --primary-foreground: 0 0% 100%;

    /* Custom accent (purple) */
    --accent: 270 67% 47%;
    --accent-foreground: 0 0% 100%;
  }
}
```

## cn() Utility Function

The `cn()` utility combines `clsx` and `tailwind-merge` for conditional class names:

```tsx
// lib/utils.ts
import { type ClassValue, clsx } from "clsx"
import { twMerge } from "tailwind-merge"

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs))
}

// Usage examples
cn("px-4 py-2", isActive && "bg-primary text-white")
cn("text-sm", size === "lg" && "text-lg", className)
```

## Extending a Component

Create wrapper components to add functionality without modifying the base:

```tsx
// components/ui/loading-button.tsx
"use client"
import { Button, ButtonProps } from "@/components/ui/button"
import { Loader2 } from "lucide-react"

interface LoadingButtonProps extends ButtonProps {
  loading?: boolean
}

export function LoadingButton({ loading, children, disabled, ...props }: LoadingButtonProps) {
  return (
    <Button disabled={loading || disabled} {...props}>
      {loading && <Loader2 className="mr-2 h-4 w-4 animate-spin" />}
      {children}
    </Button>
  )
}

// Usage
<LoadingButton loading={isSubmitting} type="submit">
  Save Changes
</LoadingButton>
```

## components.json Configuration

The `components.json` file controls CLI behavior:

```json
{
  "$schema": "https://ui.shadcn.com/schema.json",
  "style": "default",
  "rsc": true,
  "tsx": true,
  "tailwind": {
    "config": "tailwind.config.js",
    "css": "app/globals.css",
    "baseColor": "slate",
    "cssVariables": true,
    "prefix": ""
  },
  "aliases": {
    "components": "@/components",
    "utils": "@/lib/utils",
    "ui": "@/components/ui",
    "lib": "@/lib",
    "hooks": "@/hooks"
  }
}
```

> **Security**: Only use trusted registry URLs in `components.json`. Never point to untrusted third-party registry endpoints.