Smiley Face Part I
A yellow circle with a black stroke forms the head of a smiley face, with two black eyes offset symmetrically above the center. The mouth is drawn as a semicircular arc using `d3.arc()` with inner and outer radii, creating a thick path spanning from 90 to 270 degrees. The visualization is built with React (v17) rendering inline SVG, and uses D3 v6's `arc` API to compute the mouth path. The code defines all dimensions as constants, with the face radius derived from the viewport height.