This example renders a smiley face in SVG using React and D3. It draws a yellow circle for the head with a black stroke, two eye circles, and a mouth path created with D3’s `arc` function, which is chained to set inner and outer radii and start and end angles. The app imports `React`, `ReactDOM`, and `arc` from `d3`, and uses a React component to produce the SVG markup, which is then mounted into the DOM via `ReactDOM.render`.