A solution to the unsolved CSS problem of animating an element height

Post author here: this post is a bit dated, and I need to update it. While the CSS grid trick works fine, hopefully, very soon, there'll be better ways to animate an element's height.

Chromium is shipping `interpolate-size` already, which enables transitioning from/to `height: auto`. Webkit and Firefox still have to agree with this web platform addition, but I'm optimistic. So let's hope!