A single yellow circle follows the mouse cursor across an SVG canvas. The React component relies on an `onMouseMove` handler to capture pointer coordinates, which updates the circle's `cx` and `cy` properties. This example uses React 16.9 with hooks like `useState` and `useCallback`, and while D3 v5 is loaded, the visible rendering is plain SVG without any D3 functions. The initial mouse position is centered within the 960 by 500 viewport.