A React-rendered SVG smiley face that fills the browser viewport, with the face centered and scaled relative to the window dimensions. The example uses React 16.9 and D3 v7, specifically the `arc` generator to define a mouth path from an inner radius of 0 to an outer radius of 100, spanning 0 to π/2 radians. The face consists of a yellow circle with a black stroke, two eye circles offset by fixed pixel distances, and the D3-generated mouth arc. The code computes the head radius from the window height and applies the stroke width internally, with all geometry positioned via a translated SVG group.