This example displays a large, centered "Hello React!" message on a plain webpage. It demonstrates a minimal React 18.2.0 setup, loading the core `react` and `react-dom` libraries via an unpacked CDN. The `index.js` file defines a simple `App` component that renders a div with the message, and then uses `createRoot` from `react-dom` to mount that component into the `#root` element of the HTML page. The code shows the basic pattern of rendering a React component into the DOM.