STORM-376 FIXED Toast close button sometimes didn't disappear.
Reason: Each toast's panel lies on an invisible floater which is a bit bigger than the panel. Notification toasts were displayed so close to each other that the floaters were overlapped by 2 pixels. Because of the overlapping, toasts sometimes didn't receive mouse-leave events, thus not hiding their close buttons.
Fix: Increased padding between toasts by 2 pixels (from 5 to 7) to eliminate overlapping.