A smiley face drawn with SVG circles follows the mouse cursor across the full viewport. The React `useState` and `useCallback` hooks track pointer coordinates from the SVG’s `onMouseMove` event, updating a 10-pixel-radius circle’s `cx` and `cy` attributes in real time. ReactDOM renders the component into the `#root` element using React 16.9, with no fixed data source or external libraries beyond the SVG primitives.