This example shows a cheerful yellow smiley face built with D3.js, whose eyebrows animate upward and back down in a looping motion. The face is rendered as SVG elements using `d3.select`, `append`, and `d3.arc` for the mouth, while `transition()` and `attr()` handle the eyebrow movement. The code constructs the face with separate groups for eyes and brows, using plain SVG shapes like `circle` and `rect`, and runs entirely client-side with d3.v7.