Change caption margins

When I add a caption and description to the simple portfolio template, the text appears with no margins and the text is pushed against the sides of the background container.

I tried adding some custom CSS, but I’m not sure if my syntax is correct, because it doesn’t seem to be working. Below are some of the various code lines I have tried:

#foogallery-caption {margin: 5px 5px}
#foogallery-simple_portfolio-bf-caption {margin: 5px 5px}
#foogallery-gallery-781 {margin: 5px 5px}
#foogallery-gallery-781-caption {margin: 5px 5px}
#foogallery-gallery-desc {margin: 5px 5px}

Here is a link to the test page where I am trying to set up the gallery:
https://diamondrockconcrete.ca/000-2/