A React-based smiley face fills the browser window, centered dynamically with adjustable eye and mouth geometry. It renders a yellow circle with black stroke, two black eyes, and a mouth as SVG circles, using React’s declarative JSX syntax to compute positions relative to viewport dimensions. The code imports React and ReactDOM, defines constants for spacing and radii, and mounts the component to the root div. The face responds to window size since all coordinates derive from `window.innerWidth` and `window.innerHeight`.