This example displays a centered, large-scale "Hello React!" message on a plain webpage. It uses React and ReactDOM to render a single component, `App`, into the `#root` div. The component is defined with a `className` of "message", which is styled with a font-size of 13em and centered text. The code imports React and ReactDOM directly and calls `ReactDOM.render` to mount the static text. The page loads React via CDN and runs the component output through a bundled JavaScript file.