Fork of Smiley Face Part III
An SVG smiley face is drawn using React 16.9 and D3 v5, with a green circular head, black stroke, two filled eye circles, and an arc for the mouth. The `arc` generator from `d3` creates the mouth path with start and end angles. Coordinates and dimensions are computed from a fixed 960×500 viewport, with all elements positioned relative to the center using a translated `<g>` group. React renders the SVG components declaratively, while D3 provides the arc path geometry.