Smiley Face Part I
This example renders a yellow smiley face in SVG using React and D3 v7. It shows a circular face with two eyes and a semicircular mouth, all positioned relative to a central coordinate system via a group transformation. The code uses `d3.arc` to generate the mouth path, with explicit `innerRadius` and `outerRadius` values, while the face and eyes are simple SVG `circle` elements. Stroke width and radius calculations adjust the face size based on the fixed 960×500 viewport.