Fifty circles arranged vertically cycle horizontally across the screen in an animated loop. Each circle’s fill color transitions from light yellow to dark navy based on its vertical position, using a linear scale with HSL interpolation. The example demonstrates SVG shape rendering and CSS styling, with animations driven by D3 v4’s `transition` and `d3.active()`. The code uses `d3.scalePoint` for layout and `d3.scaleLinear` for color mapping, all within a single SVG canvas.