.block{
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
background-color: rgba(0, 0, 0, 0.8);
text-align: center;
padding-top: 15%;
opacity: 0;
-webkit-transition: all 0.5s;
transition: all 0.5s;
}
.block:hover{
opacity:1;
}