This example shows a small yellow circle that follows the mouse as it moves over a blank SVG canvas. The circle’s position is updated reactively through React’s `useState` and an `onMouseMove` event handler. The visualization is built with React and D3 v5, rendering an SVG element whose width and height are fixed at 960 by 500 pixels. The circle’s center coordinates are set directly from the mouse event’s `clientX` and `clientY` values, and the component is mounted using `ReactDOM.render`.