* {
    margin: 0;
    padding: 0;
}

html, body {
    width: 100%;
    height: 100%;
}
body {
    background: url(bg.jpg) center no-repeat;
    background-attachment: fixed;
    background-size: cover;
}

.logo-container {
    display: table;
    height: 100%;
    width: 100%;
}
.logo-container .logo {
    display: table-cell;
    vertical-align: middle;
}
.logo-container img {
    display: block;
    max-width: 50%;
    max-height: 50%;
    width: auto;
    height: auto;
    margin: 0 auto;
}