A circle follows the mouse cursor across an SVG canvas, updating its position in real time. The visualization uses React state to track mouse coordinates and re-render the circle’s cx and cy attributes. It imports the `arc` function from D3 but does not apply it, relying instead on React’s `onMouseMove` handler and D3 v5 for SVG rendering. The page is built with React 16.9 and renders a single unfilled circle at the pointer’s location.