html {
    background: url(bg.jpg) no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    font-family: 'Roboto', sans-serif;
}

.img-center {
    position: relative;
    width: 300px;
    margin: auto;
}