A React component renders a simple smiling face in an SVG, built from a yellow background circle, two black eyes, and a mouth shaped as a d3 arc path. The `Face` component composes smaller components (`BackgroundCircle`, `Eyes`, `Mouth`) inside a `FaceContainer` that translates the SVG group to center the face. The mouth uses `d3.arc()` with inner and outer radii and fixed start and end angles. The code relies on React 18 and d3 v7, with all proportions passed as props from the main `App` component.