Tooltip-down's negative top margin should be positive bottom margin

I guess this is used to preserve some space for the arrow the be displayed.
It shouldn't pull up the container -.75em, which might make it overlap with
whatever is above (like error messages)

Change-Id: Ie69418f62065cc697f4fb37a3db903eb2d2760e3
Merge "Tooltip-down's negative top margin should be positive bottom margin"