How to only switch the size of a picture gallery on the home page for moblie view

I need some help Squarespace community! I'm wondering if you can help me, because I cannot find anything online to help. I have a slideshow photo gallery that auto plays through the pictures on my home page. It looks fine on desktop, but the problem is that on mobile it looks horrible and I cannot figure out how to change the size for only the mobile. Again, this is on my home page, so for some reason it is more difficult I think? I want the gallery pictures smaller, but not the rest of the pictures on the cover page (or site). I'm willing to pay to get the answer as I've already wasted too much time trying to figure this thing out. Can you please help? You can check it out for yourself: hobblecreekbaptistchurch.com I look forward to your response!

Add to Design > Custom CSS

/* Mobile Resize Slideshow */
@media screen and (max-width:991px) {
.gallery-fullscreen-slideshow {
    height: 30vh !important;
}
}