To display border of a transparent Collection, press the Cmd key while moving mouse pointer over the Collection. A black frame will be displayed and the Collection can be resized by dragging the frame. Resize cursor is displayed for active Collection - click on a Collection to make it active.
To move a Collection without title bar (the title bar can be turned off in the Settings) press the Cmd key while moving mouse pointer over the Collection. The title bar will be displayed and you will be able to drag and move the Collection:
If you also enabled hiding title bar buttons you can still access the Collection menu. Press Cmd key and move mouse pointer over the Collection to make it selected, then right click near the window edge (to avoid clicking on an item):
