This example demonstrates a minimal React application that renders a centered “Hello React!” message using a large font size. It shows how React 16.10 integrates with a plain HTML page by mounting a component into a root div. The code uses `React` and `ReactDOM` from the UMD production builds, defining a functional `App` component and calling `ReactDOM.render` to attach it to `document.getElementById('root')`. Styling is handled via a simple CSS class in the HTML head, with no data or visualization logic included.