One thing that single div pieces rarely do is animate. If you can transform your div or one of its pseudo elements, that’s fair (as Lynn Fisher does with her fantastic BB-8). But you cannot directly change the opacity or transform of the individual “elements" you create inside your div, since they are not actual DOM elements.
I am a big believer of trying something a little different and interesting to learn tools you otherwise might never learn. Working with the constraints of a single div might not be great for production work, but it can be a great exercise (and challenge) to stretch your skills in a fun way. In that spirit, we’ll use this technique to explore how Custom Properties (CSS Variables) work and even provide us a path to animation inside our div.
Animating Single Div Art is a post from CSS-Tricks