A smiling face rendered as a full-screen SVG scales with the browser window. The face centers itself dynamically, with a yellow circle for the head, black stroke outlining it, and two black eyes positioned symmetrically. The React component computes dimensions from `window.innerWidth` and `window.innerHeight`, then uses SVG `<circle>` elements within a translated `<g>` group. The code defines explicit variables for eye offset, radius, and stroke width, but the mouth remains absent in the current implementation. React and ReactDOM handle the rendering into the `#root` element.