This example shows a minimal React application that renders a full-screen “Hello React!” message, demonstrating the basic setup for a React-based visualization gallery. It uses the `react` and `react-dom` production builds from unpkg to mount a functional `App` component into a root `div` via `ReactDOM.render`. The message is styled with CSS set to a large font size and centered alignment, with the logic contained entirely in an `index.js` file that imports React and ReactDOM.