Make figure.gallery.grid.item square

Site URL: https://corn-apricot-zn88.squarespace.com/

I am trying to make the figure.gallery.grid.item on a gallery section so that it is square. I have the description turned off via css, but I need the caption "on" or the overlay text disappears. I want the same vertical spacing as horizontal, but I cannot seem to get the item to be square. Is there a way to do it that would be responsive for tablet etc? 

thank you!