As for the Drop Down – I’m seeing the problem in Safari, but within Chrome and Firefox it looks fine, as you mentioned.
Changing the z-index of the Drop Down is not going to help. The problem originates with the way the animation is rendered. We make use of one of the most widely used CSS animation libraries out there call Animate.CSS. It sets an
animation-fill-mode that is required of the animations to make sure they display properly. Safari is not rendering it properly it seems. Whether it is a Safari bug or how they intend for the browser to render this fill mode I am unsure, but that is where the problem originates.
I can’t change this fill mode, as I suspect it will cause problems for the Reveal stack and the way it is supposed to work. My suggestion would to remove the Drop Down stack from within the Reveal stack and use it as-is.