A yellow circle follows the mouse cursor across an SVG canvas. Built with React, the app tracks cursor coordinates via the `onMouseMove` event and stores them in state using the `useState` hook. The `useCallback` hook optimizes the event handler, and `ReactDOM.render` mounts the component. The SVG’s circle element updates its `cx` and `cy` attributes to match the current mouse position, creating a direct, real-time visual response.