A single dark circle follows the cursor across a full-screen SVG canvas, reacting instantly to every mouse movement. The visualization uses React 16.9 with the `useState` and `useCallback` hooks to track pointer coordinates, updating the circle's `cx` and `cy` attributes via ReactDOM rendering. The example demonstrates React's declarative approach to interactive graphics, with the `onMouseMove` event handler on the root SVG element driving all state changes in real time.