Fork of Smiley face part 1
This example draws a stylized smiley face using React and D3’s `arc` API to render an SVG. It shows a yellow circle with black stroke, two black eye circles, and a mouth arc. The mouth is created with `arc().innerRadius()`, `outerRadius()`, and `startAngle`/`endAngle` set to a half-turn, while all other shapes are plain SVG `<circle>` elements. The layout centers on a fixed 960×500 viewport, with coordinates and dimensions defined as constants rather than data-driven.