.logo img {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%)
}

body {
    min-height: 100vh;
    background: url('bg-tiny.png') no-repeat center center fixed;
    ;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

html {
    height: 100vh;
}