This example renders the text "Hello D3 & React" as a full-screen message using a React component with a ref hook. The code demonstrates a minimal integration between React 19 and D3 v7, where the useEffect hook calls d3.select to set the text content of a div element. The visualization shows how to combine React's component-based rendering with D3's DOM selection API, with basic styling applied through a CSS class. The example serves as a starter template for mixing these two popular JavaScript libraries.