html, body {
    width: 100%;
    height: 100%;
}

/* for phone */
@media only screen and (max-width: 600px) {
    .container-bg {
        background-image: url("../../img/mobile_transaction_background.jpg");
        background-repeat: no-repeat;
        background-position: center;
        background-size: cover;
        width: 100%;
        height: 100%;
    }
}

/* for desktop */
@media only screen and (min-width: 601px) {
    .container-bg {
        background-image: url("../../img/transaction_background.jpg");
        background-repeat: no-repeat;
        background-position: center;
        background-size: cover;
        width: 100%;
        height: 100%;
    }
}

.mid {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}