This example renders a smiling face with D3.js and React, showing how D3’s `arc()` generator creates a mouth path while React manages the SVG elements. The face consists of a yellow circle with a black stroke, two eye circles positioned via offsets, and a mouth drawn as an arc using `innerRadius`, `outerRadius`, and angle specifications. The SVG output is produced declaratively through React’s `App` component, which renders into the `#root` div using `ReactDOM.render()`.