.ptb-item {
    width: 100%;
    height:250px;
    background-repeat:no-repeat;
    background-position: center center;
    background-size: contain;
    position: relative;
}
.ptb-item > a {
    position: absolute;
    width: 100%;
    height:100%;
}
.ptb-item.mobile {
    display: none;
}
@media (max-width: 767px) {
    .ptb-item.desktop {
        display: none;
    }
    .ptb-item.mobile {
        display: block;
    }
}