Need code to show 1 column on category pages in mobile

I'm currently building my website (I have an access PW if someone wants to look at it), and I can't figure out how to have the mobile version display single columns for category pages. A screenshot is attached. 

Here's how I'm setting it all up:
 

• I have a print store for all of my products (I'm a photographer selling prints). This includes all the product photos, descriptions and pricing that ultimately shows on my product pages. This works like a charm.
• I have portfolio page as my home page, and it shows has one photo for each category that is linked to a category page. Example, when you click on the "Best Sellers" photo on the home page, it opens a category page with all my prints that are tagged with "best sellers."
• The resulting category page is what I'm having trouble with: It looks great on the desktop, but as you can see on the screenshot the mobile looks awful because it's showing 3 columns. The images are tiny.
• Also, I would love to have this category page only show the photo, the product title and the pricing (no descriptions).
• Clicking on a photo in this category page takes you to the product for that photo, with all the description and ordering functionality.

I know there has to be a code to make this work well. Any thoughts?

Please provide website url and password.

andycrawfordphotography.com

Password: 10zlL&Wx3#8

19 hours ago, ACPhotos said:

andycrawfordphotography.com

Password: 10zlL&Wx3#8

You can use this code to Website Tools > Custom CSS

@media screen and (max-width:767px) {
body.collection-659ed54cb8004b1e1a7bf395.view-item {
.summary-item-list {
    height: auto !important;
}
.summary-item {
    position: relative !important;
    top: unset !important;
    left: unset !important;
    right: unset !important;
    width: 100% !important;
}}}

Thank you. That worked, sort of. 

Unfortunately, I've found the entire Squarespace system difficult to work with - and the mobile version of the site was a complete disaster. 

So I've canceled my subscription. Not worth the stress.