A Voronoi diagram partitions the screen into cells, each anchored by a randomly placed site. This example renders the cells as cushioned shapes by filling each polygon with a radial gradient that transitions from white at the site’s coordinates to black at the edges, visually encoding distance from the nearest site. The gradient is defined in SVG `defs` and applied via the `fill` attribute on each `path` element. The code uses `d3.voronoi` from D3 v4 to compute the polygons and positions 20 circular site markers, with the `d3-selection-multi` plugin for setting multiple attributes at once.