This example displays a large, centered “Hello React!” message in a web page. It demonstrates the basic setup for building a React application with JSX and rendering components. The code imports `React` and `ReactDOM`, defines a simple functional `App` component that returns a `div` with the class `message`, and uses `ReactDOM.render` to mount it into a root DOM element. The page loads React and ReactDOM from CDN scripts and uses a compiled `bundle.js` file to run the JavaScript.