Thanks Rose for the help! So it’s a bit finicky with the way the 1px border renders. I fiddled with this a bit more and got a crisper 1px line using below.
.single-product #swiper-unique-id-0 {border: 1px solid #e8e8e8; margin-bottom: 10px;}
.single-product .main-images {margin-bottom: 0px;}
.single-product .thumbnails-list .thumbnail-item {border: 1px solid #e8e8e8;}