css 背景图片随屏幕大小自适应全屏

    body{
    min-height: 500px;
    background: url(/xd/resources/new/uploadimage/form_bg_new.png) no-repeat left top     !important;
    background-size: auto !important;
    overflow: hidden;
    background-repeat: repeat !important;
    background-size: 100% 100% !important;
    background-attachment: fixed;
    width: 100%;
    height: 100%;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
}