Image boarder on gallery images

I want to add a small white outline to all of my gallery images that is offset so it appears on top of all of the images. With the code below I have been able to get it to work somewhat - the issue I am having with the gallery is that some of the outlines are getting cropped off with the images instead of aligning to the cropped square box. (see image). Any ideas on how I could get the outline to match up with the cropped box would be appreciated!

.sqs-gallery-block-grid .slide .margin-wrapper a.image-slide-anchor[href] img {

cursor: pointer;

outline: #fff solid 3px;

outline-offset: -20px;

}

Can you provide link to gallery?

https://donna-elle-design.squarespace.com/portfolio

password: donna

Thank you!