Let's make a face
A smiling cartoon face is drawn using SVG shapes, with two animated eyebrows that bounce upward and downward in a looping motion. The face is composed of a green circular head, two black-outlined eyes, and a mouth created with the `d3.arc` path generator. The animation is implemented using D3 v5 `transition` calls that alter the eyebrow group's vertical transform, while the static shapes are positioned via SVG attributes and D3 selections.