.background{
    width: 100%;
    height: 100%;
    position: absolute;
    opacity: 0.3;
    background-image:url(../../assets/images/background.jpg);
    background-size: 100% 100%;
    /*按比例缩放*/
    background-repeat: no-repeat;
}

.main-content-background{
    position: fixed;margin:0 auto;top: 50%;left: 50%;
    width:50%;height: 50%;
    -webkit-transform: translateX(-50%) translateY(-50%);
    -moz-transform: translateX(-50%) translateY(-50%);
    -ms-transform: translateX(-50%) translateY(-50%);
    transform: translateX(-50%) translateY(-50%);
    border:0px solid black;
}