html {
  background-image: url("http://orientacionytutoria.uaem.mx:8080/PaginaOE/imagenes/FondoPaginaCDE.png");
  background-repeat: no-repeat;
  background-position: center center;
  background-attachment: fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}

.content {
  max-width: 500px;
  min-height: 200px;
  padding: 20px;
  text-align: center;
  border: 5px solid #ffffff;
  background: rgba(255,255,255,.8);
  position: absolute;
  top: 50%;
  left: 50%;
  margin-top: -115px;
  margin-left: -265px;
}