html, body {
    height:100%;
    margin:0;
}
body {
	position:relative;
	min-width:500px;
	min-height:450px;
	position:relative;
	background-color: #bababa;
	background-image: url(../img/bgintro.jpg);
	background-repeat: no-repeat;
	background-position: center center;	
}

#contenedor {
  width: 300px;
  height: 400px;
 
  position: absolute;
  top: 50%;
  left: 50%;
 
  margin-top: -200px;   /* height/2 = 500px / 2 */
  margin-left: -150px;  /* width/2 = 500px / 2 */ 
  
  background-image:url(../img/bsnflashindex.jpg);
  background-repeat:no-repeat;
}