A circle follows the mouse cursor across the screen, shifting its center to match the pointer’s coordinates in real time. The visualization uses React’s `useState` hook to store the mouse position and an SVG `onMouseMove` event handler to update it. The circle is rendered as an SVG element with `cx` and `cy` attributes bound to the tracked position. The page uses React 16.9.0 and ReactDOM, with the SVG filling the browser window.