body
{
	background:url("css/background.png");
	background-attachment: fixed;
}

.contenido
{
	display:table;
	border:3px #666666 solid;
	background: #ddd;
	margin: 40px auto;
}

.imagen_planeta {
	position: fixed;
	top: 0px;
	left: 0px;
}

.imagen_nave {
	position: fixed;
	bottom: 20px;
	right: 20px;
}