Twenty colored rectangles bounce and slide within a fixed SVG canvas, colliding with each other and the boundaries. The animation runs on a `d3.forceSimulation` with custom forces for rectangular collision and bounding-box containment, while a drag handler lets users move any rectangle. Each particle has a random size, velocity, and direction, with a distinct color from `d3.schemeCategory20`. The custom `rectCollide` force uses a `d3.quadtree` to efficiently resolve overlaps.