A yellow smiley face is drawn as a scalable vector graphic (SVG) that fills the browser window. The face consists of a large yellow circle with a black stroke, two black eye circles, and no mouth. The code uses React and ReactDOM to render the SVG dynamically, calculating the center and radius based on the current window dimensions. The underlying data source is the static SVG markup commented out in the HTML file, which the React version programmatically recreates.