This example shows a minimal React application that renders the text “Hello React!” as a full-screen message. The app uses a single functional component defined in `index.js`, which is mounted into a `#root` div via `ReactDOM.render`. The styling is applied through a CSS class in `index.html`, and the page loads React and ReactDOM from UMD builds served by unpkg. It demonstrates the basic setup of a React project without any additional libraries or data processing.