.randbg {
    background: url('/_imgClient/B2B/csct/background/1.jpg') no-repeat;
    -webkit-background-size: 100% 100%;
    -moz-background-size: 100% 100%;
    -o-background-size: 100% 100%;
    background-size: 100% 100%;
    /*ulterior*/
    height: 100%;
    width: 100%;
    position: absolute;
}

    .randbg.bg1 {
        background-image: url('/_imgClient/B2B/csct/background/1.jpg');
    }
    .randbg.bg2 {
        background-image: url('/_imgClient/B2B/csct/background/2.jpg');
    }

    .randbg.bg3 {
        background-image: url('/_imgClient/B2B/csct/background/3.jpg');
    }
 

.randbg-overlay {
    backdrop-filter: brightness(0.7);
    position: absolute;
    height: 100%;
    width: 100%;
    z-index: 1;
}