This example renders a full-screen smiley face using React and D3 v5, with a yellow circle for the head, two black eyes, and a curved mouth drawn as an arc. The face is centered dynamically based on the window dimensions, and the mouth is created using D3’s `arc()` generator with specified inner and outer radii and angle ranges. React manages the SVG elements, while D3 provides the path calculation for the mouth, demonstrating a hybrid approach where React handles the DOM structure and D3 computes geometry.