Consider converting Expandables to details/summary markup

[anselmbradford]

The details element is a standard element that, along with the summary element, creates a "disclosure widget". This is what our expandables are doing. We could possibly gain baked in accessible features and interactions if we switched our expandables to detail/summary markup. The animating would need to be worked out, but https://css-tricks.com/how-to-animate-the-details-element/ offers a starting point.

[sonnakim]

This one can probably wait till web components work begins. Not quite sure yet if the details element will support some of the features we currently have in our expandables (see comment above, animations in particular)