Adjust tools column z-index to make the sticky header transition less jarring

The z-index is adjusted to make sure the publish button
does not cover the tools column when moving when the header becomes
fixed on top (which happens when you scroll down).

Change-Id: I32bea280f0110acea6713938b0dce09dc56bacac
Merge "Adjust tools column z-index to make the sticky header transition less jarring"