A full-screen yellow smiley face is rendered inside an SVG, centered on the viewport with its eyes and mouth positioned using fixed pixel offsets. The face adapts to the browser window by calculating its radius and position from `window.innerWidth` and `window.innerHeight`. The example uses React 18.2.0 to create SVG circle elements, with ReactDOM rendering the component into a root div. Stroke width, eye radius, and mouth radius are defined as constants, and the face is drawn with a black outline and no explicit mouth shape.