Docking tabs is inconsistent in Mac editor

Its very difficult to dock tabs next to each other in mac editor and also the white zones flicker when a tab is dragged around the screen.

This is a regression from 4.13.2 at CL 3157003

1. Open any project in the editor on Mac
2. Bring up the Output Log by going to Window -> Developer Tools -> Output log
3. Attempt to dock next to the content browser tab.

Result: Tab does not always dock next to other tabs and white outlines flicker