body {
    background-image: url("https://source.unsplash.com/random/1600x900/?green");
    background-position: center;
    background-size: 100vw;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    height: 100%;
    width: 100%;
    background-repeat: no-repeat;
}