This example shows a React application rendering a centered, large-font "Hello React!" message directly into an HTML page. It demonstrates a minimal setup for React 18, using the UMD builds of `react` and `react-dom` loaded from `unpkg.com`. The application defines a simple `App` component that returns a `div` with the message, and `createRoot` from `react-dom` mounts it to the `#root` element in `index.html`. The rendering approach relies on `bundle.js` to execute the React code, which imports `React` and `createRoot` to initialize the UI.