This example displays a simple "Hello React!" message centered on the screen. It demonstrates the basic setup for a React application using the `ReactDOM.render` method to mount an `App` component into the root `div`. The code imports `React` and `react-dom`, and the component returns a `div` with a `className` of `message` that is styled with a large 13em font size. The application relies on a production build of React 16.10.0 loaded from unpkg.