Let's Make a Face!
A smiling face, built from basic SVG shapes, animates its eyebrows upward and downward in a repeating loop. The face is centered within an SVG canvas, with a yellow circle for the head, black-outlined circles for eyes, rectangles for eyebrows, and a curved arc for the mouth. The example uses D3 v6 to construct the scene, and applies a `transition().duration(2000)` to the eyebrow group, shifting its vertical transform to create the animation.