This example shows a smiley face rendered as a yellow circle with two eyes, drawn using React and SVG. The face automatically fills the browser window by calculating its dimensions from `window.innerWidth` and `window.innerHeight`. The code uses React 16.9.0 and ReactDOM to render SVG circle elements, with coordinates for eyes and mouth positioned relative to the center via a transform. The face’s size adapts to the viewport, and the implementation builds on plain SVG primitives without additional data sources.