This example shows a resizable smiley face rendered as a full-screen SVG using React. The face fills the browser window, with a yellow circle for the head, two black eyes, and a wide smile drawn using SVG primitives. It uses React 16.9 and ReactDOM to render the SVG elements onto a root div, with dimensions and positions computed from `window.innerWidth` and `window.innerHeight`. The face automatically adapts its size and placement to the current viewport.