Full Background dengan CSS

Cara menampilkan image background full layar dengan css :

<style type="text/css">
body {
  background: url(<?= base_url(bg.png) no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}
</style>