A circle follows the mouse cursor across a full-screen SVG, changing position live as the pointer moves. The visualization uses React state and the `useState` hook to track mouse coordinates, with a `useCallback` handler for `onMouseMove` events on the SVG element. The circle’s center is set to the cursor’s client coordinates, and its fixed radius of 30 pixels is defined as a constant. The example demonstrates a minimal React-rendered interactive graphic without external data sources or charting libraries.