A React application renders a single SVG circle that follows the mouse cursor across the viewport. It uses React's `useState` and `useCallback` hooks to track pointer coordinates from the SVG `onMouseMove` event, updating the circle's `cx` and `cy` attributes in real time. The SVG canvas is 960 by 500 pixels, with the circle initially centered and a radius of 30. The code imports React and ReactDOM, relying on React's declarative state updates to re-render the circle at new positions without additional data sources.