html {
 height: 100%;
 margin: 0px;
 padding: 0px;
}

body {
  background-image: url("fondo.jpg");
  background-position: 50% 50%;
  background-repeat: no-repeat;
  background-color: #000000;
  height: 100%;
  margin: 0px;
  padding: 0px;
}

.contenido {
  width:1000px;
  height:710px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-top: -355px;
  margin-left: -500px;
}