Hi,
Create a New Component for the Lid and make it Active.
The easy way would be to create a sketch using this part of the box as your plane.

Use Project to get the outline of the outside of the box and the bit you created sticking
up.

Extrude that part as a solid object but a new Body. Don't worry if it overlaps part
of the bottom, we will fix it.

Make the inside of the lid with an Offset extrusion.


Ok last thing is to cut out those little ridges on the lip from the
lid so it will fit properly.
Make the Top Component Active.
Using the Combine tool.

Change the Operation to Cut.

Your Target Body is the one you want to cut. That is the new Lid.

Your Tool is the bottom of the box. Uncheck New Body and
Check Keep Tools

If that all worked you will have a slot for the lid to lock
into the bottom.

Should be pretty much what you wanted.
Cheers
Andrew