This example displays a static “Hello React!” message centered on the page using an oversized 13em font. It renders through React’s declarative component model, where the `App` component returns a `div` with a CSS class. The `ReactDOM.render` API mounts the component into the `#root` element, while the page loads React and ReactDOM from unpkg CDN production builds and executes the compiled `bundle.js`. No interactive behavior or dynamic data is present.