.bg_img_body{
    background-size: cover;
    background-position: center;
    background-attachment:fixed;
    position: relative;
    z-index: 1;
}

.bg_img_body::before{
    content: '';
    position: absolute;
    width: 100%;
    height:100%;
    top: 0;
    left: 0;
    background: inherit;
    filter: blur(16px);
    z-index: -1;  /* position:absoluteのせいで最前面に来てしまうため */
 }
 
.bg_img_body::after{
    content: '';
    position: absolute;
    z-index: 2;
    width: 100%;
    height:100%;
    top: 0;
    left: 0;
    background-color: white;
    background-attachment:fixed;
    opacity: 0.75;
}

.bg_img_body * {
    position: relative;
    z-index: 3;
}