This example demonstrates a smiley face whose eyebrows animate upward and downward in a looping motion. Using D3.js v5, the code constructs the face from SVG shapes—a yellow circle for the head, two circles for eyes, rectangles for eyebrows, and a path generated with `d3.arc()` for the mouth. Eyebrow movement is driven by chained `transition().duration()` calls that alternate the group’s vertical transform. All elements are appended to a centered `<g>` within an SVG canvas, with no external data source.