Change Padding Gallery Block - Custom Code

Hello!

I have an issue with the gallery block. While it looks great on mobile, the images are way too big on desktop. Id like to increase the inset / padding on desktop only to keep the images smaller while still using the Grid as I find it optimal for easy updating. 

3mrnt.com/work

What custom CSS would I need to add on the portfolio page and in the custom CSS page to increase the padding? 

You can use this code to Website > Website Tools > Custom CSS

body#collection-6425385c7e50b0397cec1483 .gallery-masonry {
    max-width: 400px !important;
}