Strange z-index behavior with scrollbars under Chrome
You may try to add -webkit-transform: translate3d(0, 0, 0). It solves my similar problem happened in mobile chrome.
I had some similar issues, and the only way to resolve I found was to apply some special styles to the webkit scrollbar in order to show it always. See http://jsfiddle.net/sinspiral/pTkQL/ with your example fixed.
This is not platform compatible (as on windows it will apply those styles too), so you might need to find a way, maybe js, to detect on which OS it is running.
.left::-webkit-scrollbar{ -webkit-appearance: none;}.left::-webkit-scrollbar-thumb { background-color: rgba(50, 50, 50, .5); border: 3px solid transparent; border-radius: 9px; background-clip: content-box;}.left::-webkit-scrollbar-track { background-color: rgba(100, 100, 100, .5); width: 15px;}