A full-window smiley face renders with React and SVG, scaling to the browser viewport. The face consists of a yellow circular head, two black eyes, and an implied mouth, all positioned relative to the viewport center. React 16.9 creates the SVG elements, while constants like `eyeOffsetX`, `eyeRadius`, and `mouthRadius` define the facial geometry. The code uses JSX within the `App` component and `ReactDOM.render` to mount the visualization to the page.