Here’s a link to the Figma demo to play with it yourself. Or, keep reading for screenshots along with explanations of what’s happening behind the scenes.
https://www.figma.com/proto/o4sxu0rEIR1zmletrxtXRn?embed_host=twitter&kind=proto&node-id=2-60&page-id=0%3A1&scaling=contain&starting-point-node-id=2%3A60&type=design