A single gray circle follows the mouse cursor across an SVG canvas, updating its position in real time. The example demonstrates a basic interactive React component that uses the `useState` and `useCallback` hooks to track mouse coordinates. The `onMouseMove` event handler updates the circle's `cx` and `cy` attributes, while D3's `range` function is imported but not actively used. The visualization is rendered entirely through React's declarative SVG elements, with no data source or animation logic beyond direct mouse tracking.