This example creates an interactive smiley face that fills the browser window, with the face centered and scaled to the viewport dimensions. The visualization is rendered as an SVG using React for component structure and D3 v5’s `arc` API to generate the mouth path. The code imports both React and ReactDOM, defines a custom `BackgroundCircle` component, and positions the eyes and mouth using computed center coordinates and offset values. The mouth is drawn with `arc()` using inner and outer radii plus start and end angles, while the face’s radius is derived from the window height and stroke width.