A circle follows the mouse across the screen, smoothly updating its position in real time. The React component uses the `useState` and `useCallback` hooks to track the mouse’s coordinates, and ReactDOM renders the result into the DOM. The example builds on a previous version and is implemented with React 16.9, relying on CDN-hosted production builds of React and ReactDOM, with no additional visualization library. The circle’s movement is driven entirely by mouse events, and the sparse `index.js` file indicates a placeholder that is completed elsewhere in the bundled source.