html {
    background: url(../img/cemento.jpg) no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;

}

body,
html {
    height: 100%;
    background-repeat: no-repeat;
    background: url(../img/cemento.jpg) no-repeat center center fixed;
    background-size: 100% 100%;
}