This example renders a responsive smiley face that fills the browser window. The face is drawn using React and SVG, with a yellow circle for the head, two black eye circles, and a mouth suggested by an empty `<g>` transform. The code calculates the face’s dimensions from `window.innerWidth` and `window.innerHeight`, centering it dynamically. It uses ReactDOM to render the SVG to the `#root` element, with the `circle` elements positioned via `cx` and `cy` offsets from the center.