Smiley Face Part III
A smiley face rendered entirely as SVG elements, composed of a yellow circular head with two black eyes and a curved mouth. React declaratively describes the visual tree while D3’s `arc` generator computes the mouth’s path, using fixed constants for dimensions like eye offset and mouth radius. The face is centered via a D3 group transform, and the code loads React 16.9, ReactDOM, and D3 v5 from CDNs.