A single circle follows the mouse cursor across an SVG canvas, tracking its exact position in real time. The visualization uses React’s `useState` hook to store the cursor’s coordinates, updated via an `onMouseMove` event handler on the `<svg>` element. The circle’s `cx` and `cy` attributes are bound to the state, causing React to re-render the shape with each movement. The code imports React, ReactDOM, and D3 v7, though D3 is not actively used beyond the script tag.