A smiling face drawn with SVG fills the browser viewport, centered and scaled to the window’s dimensions. React manages the component tree, while D3’s `arc()` generator creates the mouth path with specified inner and outer radii and angled start and end points. Static circles define the eyes, and a yellow outer circle with a thick black stroke forms the head. The code imports React, ReactDOM, and D3’s `arc` function, then renders everything inside a single `<svg>` element.