Drop Down Behind ShareThis Buttons

We are using the ShareThis plugin to display the ShareThis buttons below every post. The ShareThis buttons display on top of the CSS drop down menu. I tried adjusting the Z-index of the navigation bar as well as the container holding the posts. The tech support at ShareThis suggested adding z-index: 90000000 !imporatant; to the nav bar. I tried adding this to the main nav container as well as all of the elements, but it did not resolve the problem. Any other ideas?