A React application renders an SVG circle that tracks the mouse cursor in real time. The circle's position updates via React's `useState` and `useCallback` hooks, which handle `mousemove` events on the SVG element. The example demonstrates simple interactive rendering with D3's `arc` import unused, relying instead on React's declarative state management. The visualization uses a 960x500 SVG canvas with a fixed circle radius, showing how React can manage dynamic visual updates without explicit D3 selection or transition APIs.