This example shows a minimal React application that displays the text “Hello React!” centered on the page. It renders a single component, `App`, which returns a `<div>` with the CSS class `message`, styled with a large font size. The code imports React and ReactDOM, then calls `ReactDOM.render` to mount the component into the `#root` element of the HTML document. The page loads React and ReactDOM from the unpkg CDN, with the application logic in a separate `bundle.js` file.