A React-rendered smiley face fills the browser window, adapting its size to the viewport dimensions. The code uses React 16.9 to create an SVG with a yellow circle for the face, two black eyes, and relies on `stroke-width` and `stroke` attributes for the outline. It does not include a mouth, despite the title, and calculates the face radius from the window height. The SVG elements are positioned using a `<g>` transform to center the composition.