This example overrides a static HTML page with a React-rendered heading. Initially, a yellow SVG circle with black stroke and two inner circles represents a smiling face, hardcoded with coordinates. The `index.js` script clears all existing DOM content and mounts a React component saying “Hello, world.” It loads React via UMD production bundles and uses `createRoot` from `react-dom/client`. The code demonstrates a minimal React integration replacing static SVG markup.