Smily Face
This example builds a smiling face from basic SVG primitives centered in a 960-by-500 viewport. It uses React to render the face, with D3’s `arc` generator creating the mouth path between specified angles. The face comprises a yellow circle with a thick black stroke, two smaller circles for eyes, and a rotated group that positions the mouth. All shapes are drawn with hardcoded coordinates, showing how React and D3 can combine for simple geometric visualizations without external data.