Two animated SVG panels demonstrate D3 selections and data joins. The top panel shows black circles on a white background, while the bottom panel renders the same dataset in white on black, driven by a 60fps interval. Each frame regenerates data via `makeData`, using trigonometric functions like `Math.tan` and `Math.cos` to animate circle positions and radii. The `vizDraw` function applies a D3 data join with `selectAll('circle').data().join('circle')` to update attributes, while `d3.range` generates the underlying sequence of values.