.container {
width: 100%;
height: 100%;
position: absolute;    
margin:auto;
top:0;
bottom:0;
left:0;
right:0;
background-color: #000;
}

img {
max-width: 100%;
max-height: 100%;  
position: absolute;
margin:auto;
top:0;
bottom:0;
left:0;
right:0;
}