html, body {height: 100%;}
body {
  margin: 0;
  padding: 0;
  position: relative;
  min-width: 800px; 
  min-height: 600px; 
  background-color: #fff;
}
.centerMiddle {
  margin: -300px 0 0 -400px;  
  position: absolute;  
  top: 50%;  
  left: 50%;  
  width: 611px;  
  height: 479px; 
  background-color: #fff;
}