A circle follows the mouse cursor across a full-screen SVG, updating its position in real time to mirror the user's pointer. The React app uses the `useState` hook to track mouse coordinates and an SVG `onMouseMove` event handler to update the circle's `cx` and `cy` attributes. Built with React and ReactDOM, the visualization renders solely with SVG elements and relies on `window.innerWidth` and `window.innerHeight` to size the canvas.