I'm trying to get the image to fade to black and to display a + sign in the center on hover but it isn't working.
.block-img img {
width:710px;
margin-bottom:50px;
position:relative;
}
.block-img img:hover:after {
opacity: 1;
}
.block-img img:after {
box-sizing: border-box;
content:"+";
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
background: black;
opacity: 0;
-webkit-transition: opacity 100ms ease-out;
transition: opacity 100ms ease-out;
color: white;
}