This example demonstrates a happy face with a yellow circular head, black outline, two eyes, and a mouth, sized to fill the browser window. It uses React to render the SVG elements, computing the dimensions and positions based on the viewport’s width and height. The code relies on React 16.9 and ReactDOM to render the `<svg>` container and its nested `<circle>` shapes, with the head positioned via a `<g>` transform. The face’s proportions are derived from the window size rather than static data.