A smiley face rendered as a yellow SVG circle follows the mouse cursor across a 960-by-500 viewport. Built with React and D3 v5, the app uses React’s `useState` hook to track cursor coordinates from an `onMouseMove` event on the SVG element, and the `arc` function from D3 is imported though not directly used in the visible code. The face updates its center position in real time, demonstrating a simple React-D3 integration for interactive graphics.