This code adds multilayer parallax to a site. Specifically, as the user scrolls down through the infinite cosmos, enjoying the view of the Milky Way, objects fly past at different speeds as if one was falling through space and crashing onto Earth, coming to rest peacefully in the mountains during an alpine sunset.

The key to understanding multilayer parallax using pure CSS involves understanding transforming the browser into a virtual 3D environment. This allows you to make different layers, which when the user scrolls, move at different speeds.