How to add borders around slideshow gallery

I'm looking to add a custom svg border around a gallery slideshow. I've tried the following code blocks, but nothing seems to work.

.gallery-slideshow-item-wrapper, .gallery-slideshow-item {
    background-size: 100% 100%;
    background-image: url(https://trumpet-plums-238e.squarespace.com/s/backgroundtest.svg);}

Hi,

Can you share link to page where you use slideshow? We can check easier