A single yellow circle follows the mouse cursor across an SVG canvas. The example combines React state management with D3’s rendering capabilities, using the `useState` hook to track cursor coordinates and an SVG `onMouseMove` event handler to update them. The circle’s position is updated reactively on every mouse movement, demonstrating a simple interactive data binding between user input and a rendered visual element. The code imports React and ReactDOM directly, while D3 v5 is loaded via a CDN script tag for integration.