On a listing detail page, we have a great feature that includes 4 images on the left side of the page that allows users visual insight quickly into a home. A Quickview button allows them to see up to 4 images of the property at any given time.
To change the color of the Quickview button, you can use this code:
.sidx-container .sidx-photo-array button {
color: #hexcode !important;
border: 1px solid #hexcode !important;
background-color: #hexcode !important;
}
The background color is set to white, and you don't have to change all of it if you don't want to. Whatever suits your needs.
Remember, place this code in the custom CSS box under Settings > Design. Clear your caches and check your web page in an incognito browser to see the change!