Drop Item Inventory

I have set up the drag and drop for the items.

How can i make it so when an item is dragged outside of the scroll box (Inventory) the item is dropped? I have already got the dropping setup i just need to put it all together.

GIF - Screen capture - 3ce9a91b81cf3ee2646d0764a61c7259 - Gyazo

Have some kind of Master UI Widget that spans across the whole screen. You can implement the drop event there. Also a nice bonus is the ability to compose the whole ui with the UMG designer

I have done some messing around with it and this is what i have got.

GIF - Screen capture - 2de4bb8eaacf053da343f430750a84e4 - Gyazo

At the moment the items can drop on any border including itself how can i stop this so it can only be dropped when dragged on to the left border?