A yellow circle with a black outline follows the mouse cursor across an SVG canvas. Built with React and D3 v6, the app tracks the pointer's `clientX` and `clientY` coordinates on a `mousemove` event, updating the circle's `cx` and `cy` properties via React state. The `BackgroundCircle` component renders the static yellow circle, while the main `App` component manages the interactive position updates. The visualization demonstrates real-time data binding between user input and SVG element attributes.