html {width:100%;height:100%;}
body {width:100%;height:100%;background-color:#17a69e;}

.logo {
position:absolute;
left:50%;
margin-left:-145px;
top:50%;
margin-top:-30px;
transition-duration: 1s;
}
.logo:hover {
opacity:50%;
transition-duration: 1s;
}