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A React progress bar component built on Radix UI's Progress primitive with customizable styling and smooth transitions.

## Key Components

- **Progress** - Main progress bar component with forwarded ref support
- **ProgressPrimitive** - Radix UI progress primitives for accessibility and behavior
- **cn utility** - Class name merging utility for styling

## Usage Example

```typescript
import { Progress } from "./progress"

export default function ProgressDemo() {
  const [progress, setProgress] = React.useState(13)

  React.useEffect(() => {
    const timer = setTimeout(() => setProgress(66), 500)
    return () => clearTimeout(timer)
  }, [])

  return (
    <div className="w-full space-y-4">
      {/* Basic progress bar */}
      <Progress value={progress} className="w-[60%]" />
      
      {/* Custom indicator styling */}
      <Progress 
        value={85} 
        indicatorClassName="bg-green-500"
        className="h-4 rounded-lg"
      />
      
      {/* Loading state */}
      <Progress value={undefined} />
    </div>
  )
}
```

The component supports standard HTML attributes, custom className for the root element, and `indicatorClassName` for styling the progress indicator. The progress indicator animates smoothly via CSS transforms and accepts values from 0-100.