A full-screen SVG circle follows the mouse cursor in real time, remaining centered on the current pointer position. The example uses React with the `useState` and `useCallback` hooks to track cursor coordinates and update the circle's `cx` and `cy` attributes. React DOM renders the SVG element, which listens for `onMouseMove` events, and the circle's radius is fixed at 30 pixels. The visualization demonstrates a simple interactive pointer-tracking effect with no external data source.