This example demonstrates fundamental DOM manipulation with D3.js by rendering an interactive smiley face whose eyebrows move. It shows how to select and modify SVG elements dynamically, creating a playful character that responds to browser dimensions. The code uses D3 v5's `select` and `arc` methods to construct shapes, with SVG attributes for width, height, and corner radius set programmatically. The visualization adapts to the full viewport size, with a fixed-position body and hidden overflow ensuring the canvas fills the entire screen.