A small yellow circle tracks the mouse cursor across a blank SVG canvas in real time. The example demonstrates a simple interactive follower effect, where the circle’s center coordinates update on every mouse movement event. Built with React and D3.js v5, it uses `useState` to store cursor position and an SVG `onMouseMove` handler to trigger state changes. The rendering approach is purely declarative, with the circle’s `cx` and `cy` attributes directly bound to the current mouse coordinates, and D3 is imported but not used beyond the basic setup.