A simple React component tracks the mouse position and renders a single circle that follows the cursor across an SVG canvas. The circle's center coordinates are updated via React state on every `mousemove` event, using the `useState` and `useCallback` hooks. D3.js v5 is loaded but not actively used, while the rendering relies on React's declarative SVG elements rather than direct DOM manipulation. The example demonstrates basic interactivity and state-driven updates in a React-D3 integration.