body:before {
    content: "";
    width: 100%;
    background-image: linear-gradient(to top, rgba(255, 255, 255, 0.3) 0%, rgba(255, 255, 255, 0.3) 100%), url(../img/mainvisual.jpg);
    background-size: cover;
    background-position: bottom;
    background-repeat: no-repeat;
    display: block;
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    z-index: -1;
}