A React component renders an SVG circle that follows the mouse cursor across a 960 by 500 pixel canvas. The circle starts at the center and updates its position on every `mousemove` event via React's `useState` and `useCallback` hooks. The `handleMouseMove` callback reads the event's `clientX` and `clientY` coordinates to set the new circle center, using ReactDOM to mount the app. No data source is involved; the visualization simply tracks pointer movement in real time.