Toolbar hovering style is applied to other toolbars when dragging

[stevenmasci]

Bug report

• Package version(s): v1.1.1
• Browser and OS versions: Google Chrome, Fedora 27

Steps to reproduce

1. Drag a window to a new location.
2. Look closely at the toolbars of all the windows when performing the drag.

Actual behavior

The hovering css style is applied to another window's toolbar. Depending on the layout, another window's toolbar will become highlighted during the process of dragging windows to particular positions.

Expected behavior

While dragging, no other window toolbars should become highlighted.