This example renders a full-screen SVG of a simple smiley face using React and D3. It shows a yellow circle with a black outline, two eye circles, and a mouth arc created with the `d3.arc()` API. The React component computes dimensions from `window.innerWidth` and `window.innerHeight`, positioning all elements relative to the center. The code demonstrates how D3 shape generators can be integrated within a React-rendered SVG.