A smiling face rendered in SVG uses D3.js to construct its geometry, while CSS custom properties define all visual dimensions and positions. The face, eyes, eyebrows, and mouth are created by appending SVG shapes with D3's selection API. Eyebrow movement is prepared through commented-out D3 transition code, with offsets stored as CSS variables. The example demonstrates how D3 v5 DOM manipulation can combine with CSS variables for styling, though the animation logic remains incomplete.