Collapsible sections need to animate height from 0 to full content height. CSS transitions don't work well with `height: auto`. You must measure the content height and set explicit pixel values to animate smoothly.
animateHeight(element, open, duration) measures the element's scrollHeight, sets an explicit height, animates to
the target height, then resets to `auto` (or `0`) after the animation. It returns a Promise that resolves when the animation completes.
Collapsible, Accordion, ExpandableSection, TreeView, Details