DraggableElement: Fix regression on selectors
DraggableElement: Fix regression on selectors

Fixing regression from I1facc746305fec12 where Less notation lead to
invalid CSS selectors.

Change-Id: I08a9e8725ad1cf69c8ece0a7055086d7384e79ec

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui