Let's make a face with D3.js!
A smiley face built with D3.js animates its eyebrows in a looping vertical motion. The example demonstrates fundamental DOM manipulation by selecting an SVG canvas and appending circles, rectangles, and a mouth path using `d3.select` and `d3.arc`. Eyebrow movement relies on chained `transition().duration(2000)` calls that alternately shift the eyebrow group’s `transform` attribute up and down. The face is centered via a translated `<g>` element, with static geometry defined by numeric constants for eye spacing, radius, and eyebrow dimensions.