This example demonstrates a minimal React application that renders the text "Hello React!" centered on the page with a font size of 13em. The code uses React's `ReactDOM.render()` function to mount an `App` component, defined as an arrow function returning a `div` element, into the HTML element with the ID "root". The page loads React 16.13.1 and ReactDOM from the unpkg CDN, with the JavaScript logic contained in `index.js` and executed through `bundle.js`.