This example shows a single circle that follows the mouse cursor across the full browser window, demonstrating real-time interaction in a React-based SVG visualization. The circle’s position updates continuously as the user moves the mouse, driven by React’s `useState` and `useCallback` hooks to store and update the cursor coordinates. It uses ReactDOM to render an SVG `<circle>` element, with `onMouseMove` handling events on the SVG root, and the initial mouse position set to the center of the viewport.