.container {
    width: 80%;
    height: 80%;
    position: absolute;    
    margin:auto;
    top:0;
    bottom:0;
    left:0;
    right:0;
    background-color: #fff;
    }
img {
    max-width: 100%;
    max-height: 100%;  
    position: absolute;
    margin:auto;
    top:0;
    bottom:0;
    left:0;
    right:0;
    }