Let's make a face with D3.js!
A smiling face built from SVG shapes uses D3.js arcs and gradients. The code draws a circular head with a linear gradient, two elliptical eyes, and a mouth created with the `d3.arc` generator. Both the face and features apply custom `linearGradient` definitions. The visualization demonstrates basic D3 selections and shape helpers to assemble a simple, stylized character.