A single gray circle tracks the mouse cursor in real time within an SVG canvas. The visualization shows how React state updates can drive direct SVG element positioning. The `App` component captures mouse coordinates via the SVG `onMouseMove` handler, stores them with `useState`, and re-renders the circle’s `cx` and `cy` attributes on every movement. Built with React 18 and D3 v7, the example renders purely through SVG elements without additional data sources or animation logic.