A smiling face rendered in SVG animates its mouth and eyelids using D3 transitions. The code draws a yellow circle for the head, positions two eyes, and constructs an arc-based mouth with `d3.arc()`. The mouth transitions between two arc radii over two seconds, while rectangular eyelids move up and down using chained `.transition().duration()` calls. Built with D3 v5 selections, the example demonstrates SVG shape manipulation and timed animations within a React-free HTML page.