This example renders a full-screen smiley face using React and SVG. The face consists of a large yellow circle for the head, two black circles for eyes, and a mouth drawn as a thick black arc. The code uses React's `ReactDOM.render` to mount the SVG into the DOM, with dimensions and positions computed from `window.innerWidth` and `window.innerHeight`. All shapes are positioned relative to a center point using an SVG `<g>` transform.