A yellow smiley face fills the browser window, rendered as a single large circle with two smaller eye circles inside a central group. The face adapts to the viewport size by computing its dimensions from `window.innerWidth` and `window.innerHeight`, setting the face radius to half the window height. Built with React and ReactDOM, it uses static SVG circle elements positioned via the `transform` attribute, with coordinates calculated from constants for eye offset, eye radius, stroke width, and mouth radius. The code does not include any interactive or animated behavior beyond the initial static render.