Hello,

You need to add the class .woodmart-archive-shop with the CSS you are using and the code will look like:

.woodmart-archive-shop .product-grid-item{
background:#fff;
border-radius:0px;
margin:15px;
box-shadow:0 0 1px rgba(0,0,0,0.5);
padding-bottom:15px;
padding-top:15px;
}

.woodmart-archive-shop .product-grid-item:hover {
border: none !important;
box-shadow:none !important;
}

.woodmart-archive-shop .product-grid-item {
max-width: 30.8%;
}

This code will not affect the homepage. But it will work the same on the product page and the shop pages and will also affect the related products items as well.

Best Regards.