A plain SVG circle follows the user's mouse cursor across a 960-by-500 canvas. The React component tracks `clientX` and `clientY` from a `mousemove` event handler, updating state to reposition the circle's `cx` and `cy` attributes. The example uses React's `useState` and `useCallback` hooks, with D3 v7 loaded for potential supplementary utilities, though rendering relies solely on SVG elements and React's declarative updates.