This example uses D3.js to build a smiley face whose eyebrows animate. The code selects an SVG element, sizes it to the full browser window, and appends a rounded rectangle as the background. It demonstrates fundamental DOM manipulation by chaining D3 methods like `select` and `append` to create the face’s parts, with the eyebrow movement driven by simple data-driven updates in the same SVG structure. The project relies on D3 v5 and renders entirely as SVG.