A smiley face is rendered in an SVG using React components that compose a yellow background circle, two eyes, and a mouth. The face is centered and parameterized by properties like eye offset, radius, and stroke width, which are passed down from a top-level `App` component. React (v16.7) manages the component hierarchy, while D3 (v7) generates the mouth path via the `arc` generator, defining an inner and outer radius with a specified angular range. The SVG container is produced by `FaceContainer`, which translates the coordinate system to the face’s center.