A red circle follows the mouse cursor inside a fixed-size SVG viewport, responding to every pointer movement across the canvas. The application uses React hooks, specifically useState and an onMouseMove event handler, to track and update the circle's x and y coordinates in real time. The circle is rendered as an SVG element with a red fill and black stroke, positioned based on the mouse position state. The example demonstrates interactive SVG rendering with React's declarative state management, using ReactDOM to mount the component into the page.