Happy Face HTML
This example uses React and SVG to render a classic happy face. The code draws a yellow circle using a custom `BackgroundCircle` component, positions two black eyes, and adds a smile with a `d3.arc` path. D3's `arc()` API defines the mouth’s inner and outer radii and its start and end angles. The SVG is generated imperatively with React’s JSX syntax, and the layout is centered on a 960 by 500 canvas. The example demonstrates combining declarative React components with D3’s geometry helpers for simple static graphics.