IE z-index bug

In short, z-index is broken in IE compared to other browsers because IE starts positioned elements with z-index 0. The fix is to make the parent of the positioned element have a z-index at least 1 higher.

• http://www.quirksmode.org/bugreports/archives/2006/01/Explorer_z_index_bug.html
• http://tjkdesign.com/articles/z-index/teach_yourself_how_elements_stack.asp