A yellow smiley face rendered with SVG circles and a d3.arc path follows the mouse: a small red circle tracks the cursor across the screen, while the face’s background, eyes, and mouth are positioned around the viewport center. React state updates the cursor-following circle’s coordinates via a mouse move handler, and the d3.arc function in Mouth.js computes the smile path. The example uses React 17, D3 v7, and SVG rendering.