create borders around galleries in essential grid

I’d like to create borders around the individual galleries I set up in my essential grid. They look too busy superimposed on top of my background parallax picture for my “Gallery of Tile Installations”. Here is the URL: https://fjarildesigns.me/for-the-home/

I’d also like to know how to adjust the padding/thickness of the border as well as the color.

Please mark this as private.

Thanks