body{
    background-image: url("/images/shared/bg-cloud-paars.jpg");
}

.thumbrect {
    float:left;
    position: relative;
    width: 100%;
    padding-bottom : 67%; /* make same as width for a 1:1 aspect ratio */
    margin:1.66%;
    background-position:center center;
    background-repeat:no-repeat;
    background-size:cover; /* you change this to "contain" if you don't want the images to be cropped */
    background-color: rgba(0, 0, 0, 0.5);;
}