InDesign 17.3 How do I center a Rectangle inside a Table Cell?

I've created an InDesign document, added a Text Frame, and inserted a Table into that Text Frame.

I've drawn a 4cm x 4cm rectangle using the Rectangle Tool, outside of the Table.

I'd like to center that rectangle in a Table Cell, but cannot find any way of doing so. I've tried converting the cell into a Graphics Cell, but no matter what I do, I cannot center the rectangle in a cell. None of the Align option work.

Any help on the procedure to do this? I've attached the document that shows what I'm trying to do.

Thanks,