This example renders a React SVG visualization of a smiley face that responds to mouse movement. The code uses React 16.9.0 and ReactDOM to create a single yellow circle that tracks the cursor position via an `onMouseMove` event handler on the SVG element. The circle’s coordinates are derived from window dimensions (`window.innerWidth` and `window.innerHeight`), though the circle radius is fixed. The visualization is a minimal, interactive demonstration of using React’s declarative rendering with SVG for real-time user input.