This example shows a yellow smiley face centered on the screen, with black outlined eyes and a curved mouth, all rendered as SVG shapes. The face’s size and position adapt to the browser window using `window.innerWidth` and `window.innerHeight`. The code uses React with JSX to declare the SVG elements, and the mouth is generated with the `d3.arc` function, which computes a path from angular coordinates. The face is composed of circles for the head and eyes, while the mouth is drawn as a thick arc with a dark fill.