This example demonstrates how to integrate React with D3, rendering a static smiley face using D3’s SVG generation inside a React component. The D3 code creates a yellow circle with `d3.arc` for the mouth and simple SVG circles for the eyes. Separately, a React `useEffect` hook updates the DOM text content to display "Hello D3 & React." The project uses React 19, `react-dom/client`, and D3 v7, with the component managing its own ref via `useRef` to attach D3 selections.