#usb {
    background-image: url(../images/usb_1920.jpg);
    height: 764px;
    background-position: center -30px;
}

@media screen and (max-width: 1366px) {
    #usb {
        background-image: url(../images/usb_1366.jpg);
        height: 593px;
        background-position: center 5px;
    }
}

@media screen and (max-width: 960px) {
    #usb {
        background-image: url(../images/usb_960.jpg);
        height: 572px;
        background-position: center 43px;
    }
    #usb.section .center {
        top: 6em;
    }
}

@media screen and (max-width: 640px) {
    #usb {
        background-image: url(../images/usb_640.jpg);
        height: 497px;
        background-position: center 3px;
    }
    #usb.section .center {
        top: 5em;
    }
}