- Set `display: none` on the content of a Slider when it is fully
   collapsed, so that the DOM nodes are removed from keyboard navigation
   order

 - Make the collapse animation work more reliably across browsers by
   forcing a synchronous layout after changing the DOM node's height
   from "auto" to a fixed pixel size. In Chrome and Firefox neither
   `setTimeout(callback, 0)` nor `requestAnimationFrame` reliably
   ensured that the browser "saw" the change from "auto" =>
   fixed height instead of "seeing" a change from "auto" directly to 0,
   which does not get animated