See demo on Codepen: https://codepen.io/comehope/pen/pOgEdO
Watch interactive video on Scrimba: https://scrimba.com/p/pEgDAM/c86q9S3
Read annotated source on Segmentfault(zh-cn): https://segmentfault.com/a/1190000016145099
Inspired by: Rachel Bull https://codepen.io/rachel_web/pen/JKzrav