This example demonstrates a minimal integration of React and D3, displaying the text "Hello D3 & React" in a large, centered message. It uses a React `useRef` hook to get a reference to a div, and a `useEffect` hook to call `d3.select` on that reference to set the text content. The app is rendered using React's `createRoot` from `react-dom/client`, with D3 v7 and React 19 imported via an import map.