A yellow circle follows the mouse cursor across a blank, full-window SVG canvas. The example demonstrates a simple interactive mouse-follower pattern where the circle’s center position is updated in real-time based on pointer movement. Built with React and D3 v5, it uses React’s `useState` hook to track mouse coordinates from an `onMouseMove` event, then renders the circle via SVG. D3 is imported solely for its `arc` function, though it is not used for the visualization’s core behavior.