This example displays a full-screen message reading “Hello React!” in large, centered text. It demonstrates a minimal React application setup using React 16.13.1 and ReactDOM. The code defines a simple functional component, `App`, and renders it into the `root` DOM element via `ReactDOM.render`. The page relies on CDN-loaded React and ReactDOM production builds, with styling applied through a CSS class in the HTML file. No data or interactive visualization is present; it serves purely as a starter template for integrating React into an Observable-style gallery environment.