This example shows a scalable smiley face built from reusable React components, with its size and position adapting to the full browser window. The face consists of a yellow background circle, two black eyes, and a D3-generated mouth arc, all composed through nested functional components like `Face`, `BackgroundCircle`, `Eyes`, and `Mouth`. Rendering uses SVG within a React tree, while the mouth shape is created with the `d3.arc()` API, setting inner and outer radii and angular ranges. The code applies React 16.9 and D3 v6, with prop-driven customization for all facial features.