Fork of Let's make a face with D3.js!
A smiley face built with D3.js animates its eyebrows upward and downward in a looping transition. The code uses `d3.select`, `d3.append`, and `d3.arc` to construct SVG shapes—a yellow circle for the head, two eyes, rectangular eyebrows, and a mouth—within a centered group. The eyebrows move via chained `transition` and `.attr` calls over a two-second duration, demonstrating fundamental DOM manipulation in D3 v5.