A single yellow circle tracks the mouse cursor across an SVG canvas, returning to the center when the pointer leaves the window. The visualization is built with React state management, using `useState` and `useCallback` to update the circle’s `cx` and `cy` coordinates on every `mousemove` event. ReactDOM renders the SVG directly, while the circle’s position is derived from the event’s `clientX` and `clientY` values. No external data is involved; the example demonstrates real-time user interaction with D3’s scalable vector graphics rendered through the React component lifecycle.