A simple smiley face rendered with SVG in a React component hierarchy. The face uses a yellow background circle, two eyes, and a curved mouth drawn with `d3.arc`. Each facial feature is a separate React component (`BackgroundCircle`, `Eyes`, `Mouth`) composed inside a `FaceContainer` that centers the drawing. The example demonstrates reusable React components with D3’s arc generator for the mouth path, using fixed dimensions and props to control geometry.