CSS
.wrap{width:100vw;height:100vh;background: rgba(0,0,0,0.3);position: fixed;top:0;left:0;text-align: center;}.wrap img{vertical-align: middle;max-height: 90vh;max-width: 90vw;}.wrap:after {display: inline-block;content: ”;width: 0;height: 100%;vertical-align: middle;}
html
<div class=”wrap”> <img src=”timg.jpg” alt=”” /> </div>