This example demonstrates a minimal React application that renders a static "Hello React!" message to the browser. The code defines a functional `App` component using JSX syntax, which is then mounted to a root DOM element via `ReactDOM.render`. The setup uses React 16.13.1 and ReactDOM from UMD builds, with a separate `bundle.js` file, indicating a build step. A plain-text CSS class controls the large font sizing and centering of the displayed message.