A React application renders a single small circle that follows the mouse cursor inside an SVG canvas. The code uses the React `useState` hook to track the cursor's client coordinates, updating the circle's `cx` and `cy` attributes on every `onMouseMove` event. The SVG is 960 by 500 pixels, and the circle has a fixed radius of 30. The page loads React and ReactDOM from the unpkg CDN, while the application itself is compiled into `bundle.js`.