<style type="text/css">
body{
	width: auto;
    height: auto;
	background-color: slategray;
	overflow: auto;
}
img {
   position: absolute;
   top: 50%;
   left: 50%;
   width: 500px;
   height: 500px;
   margin-top: -250px; /* Half the height */
   margin-left: -250px; /* Half the width */
}
</style>