Add background to product thumbnails

/* use this code to add background color */
.ecwid-productBrowser-productsGrid-v2 td.ecwid-productBrowser-productsGrid-productInside {
    background-color: #FFFFFF !important; /* change the color code to any you like */
}

/* or this code to add background image */
.ecwid-productBrowser-productsGrid-v2 td.ecwid-productBrowser-productsGrid-productInside {
    background-image: url("image_url") !important; /* add your image URL instead of image_url */
}