01. face with D3.js
A yellow smiley face drawn with SVG circles, rectangles, and an arc path is centered in the viewport. D3.js selections append the facial features, while a chained `transition` with a two-second duration repeatedly moves the eyebrow group up and down. The code uses D3 v5’s `select`, `arc`, and `attr` to construct the face from hardcoded dimensions, demonstrating basic DOM manipulation and animation without external data.