This example shows a responsive smiley face built entirely from circles positioned to form the eyes, nose, mouth, and face outline. It uses D3’s `select` and data joins (`join('circle')`) to render seven SVG circles, with coordinates and radii computed relative to the container’s `clientWidth` and `clientHeight`. The code sets each circle’s fill color and opacity directly from a static data array, and the SVG background uses a pale green tone.