A simple interactive visualization renders a single SVG circle that tracks the user's pointer across the browser viewport. The circle is drawn using React's virtual DOM, with its center coordinates updated via a `useState` hook and a mouse event handler. The app uses `window.innerWidth` and `window.innerHeight` to set the full-screen SVG dimensions. React and ReactDOM are loaded from CDN, and the component re-renders each time the mouse position changes, creating a responsive follower effect.