Hello D3.js!
A cheerful face with yellow circular head, black-outlined features, and a smiling arc mouth is drawn using SVG. The eyes and eyebrows animate upward and back down repeatedly using chained `transition().duration()` calls. Built with React and D3 v6, the example selects the SVG element, computes dimensions from its attributes, and uses the `arc()` generator from D3 to create the mouth path. The code demonstrates basic D3 selections, attribute manipulation, and timed animations.