A smiling face rendered with React and SVG adapts to fill the browser window, with a yellow circle, black outline, and two eyes positioned symmetrically around the center. The code uses ReactDOM to render SVG elements, calculating coordinates based on `window.innerWidth` and `window.innerHeight`. The smile’s mouth is omitted, leaving only the head and eyes visible. React 16.9.0’s production build and ReactDOM manage the component hierarchy, while the SVG viewport scales dynamically to the viewport size.