A circle follows the mouse cursor across a 960-by-500 SVG canvas, updating its center position in real time. Built with React using the `useState` and `useCallback` hooks, the app listens for `onMouseMove` events on the SVG element and passes the cursor's `clientX`/`clientY` coordinates to the circle's `cx` and `cy` attributes. The visualization uses D3.js version 5 primarily for the SVG rendering within a React framework, with no external data source.