A circle follows the mouse cursor across an SVG canvas, updating its position in real time. The React app tracks mouse coordinates via an `onMouseMove` event handler and stores them in state using the `useState` and `useCallback` hooks. The circle’s `cx` and `cy` attributes are bound to that state, and React re-renders the SVG element on every move. The example uses React 16.9 and renders directly to the DOM through `ReactDOM.render`.