Hide first image in gallery on mobile if collection/not block

On nathanleebush.com/cinematographer, I put a vertical image as the first item in the gallery to call out my clients list and as a kind of hack to show off the name of the page. But in mobile a vertical image takes a huge amount of real estate. Is there a way to not show the image?

My template is Forte, and so this gallery page does not use blocks, it seems like, so a lot of the CSS coding solutions I see aren't applicable.

@herzog Add to Home > Design > Custom CSS

@media screen and (max-width:640px) {
body#collection-5ba509af652dea4834b80b3a .slideshow .sqs-wrapper .slide:first-child {
    display: none;
}
}