css background image cover center

1html { 
2  background: url(images/bg.jpg) no-repeat center center fixed; 
3  -webkit-background-size: cover;
4  -moz-background-size: cover;
5  -o-background-size: cover;
6  background-size: cover;
7}

1body {
2  background-position: center;
3  background-repeat: no-repeat;
4  background-size: cover;
5}

1body {
2  background-position: center;
3  background-repeat: no-repeat;
4  background-size: contain;
5}