This example shows a React component that renders the text "Hello React!" centered on the page. The code defines an `App` functional component using JSX and mounts it with `ReactDOM.render` into a root div. It imports `React` and `ReactDOM` from the React libraries and applies a CSS class for large font sizing. The example demonstrates basic React rendering with a static message, using React 16.10.0 and ReactDOM from a UMD build.