A smiling face rendered in SVG combines React components with D3's arc generator. The `BackgroundCircle`, `Eyes`, and `Mouth` components define circles and a path, while D3's `arc()` creates the mouth with controlled inner radius, width, and start/end angles. React handles component composition and state, passing numeric props for positioning and dimensions. The final SVG is mounted via ReactDOM, using fixed coordinates centered on a 960×500 canvas.