This example shows a full-screen smiley face rendered as a yellow circle with a black outline, two eye circles, and a curved mouth, positioned at the center of the viewport. The face is built declaratively using React components that output SVG elements, with position and size values computed from the browser window dimensions. It uses React 16.9 and ReactDOM to mount the SVG tree into the DOM, while relying on plain SVG circle elements and a `<g>` transform for centering. No animation or interaction is present.