Solid Edge mate problem

I have designed here a jewellery box. The lower tray has been locked into position in the base part.
I am having trouble mating the upper tray into position. I have mated it partially but not correctly.
I want to make the upper tray sit on top of the lower tray and be able to slide side to side above the lower tray as if it was just sitting on it.

I have been trying to research this for some time but I am stuck, any help would be appreciated.

Pic also attached of actual construction to this point.

Andy