This example builds a smiling face in SVG using D3.js v5 and React, with a yellow circle for the head, two eyes, and an arc-based mouth. The code uses `d3.arc` to generate the mouth path and `d3.select` to append and style elements. An animated eyebrow movement is achieved with chained `transition` calls that shift a group containing two rectangles up and down over two-second durations. The face is centered via SVG transforms, with positions calculated from the viewport dimensions.