You can see in this screenshot, the menu containing \"hi\" on each line is popping under body elements and also under a button on the screen.
Figured it out, the problem was I had a transform3d on the navbar:
-webkit-transform: translate3d(0, 0, 0);
Removing this fixed it. I noticed that when I removed the translate3d that the computed style of the navbar would cause the z-index to go from 0 to auto.
Not sure if this is intended behavior?
Hope this helps someone else down the line.