círculo transparente en un div
div{
position:relative;
width:500px; height:200px;
margin:0 auto;
overflow:hidden;
}
div:after{
content:'';
position:absolute;
left:175px; top:25px;
border-radius:100%;
width:150px; height:150px;
box-shadow: 0px 0px 0px 2000px #E3DFD2;
}
body{background: url('https://farm9.staticflickr.com/8760/17195790401_ceeeafcddb_o.jpg');background-size:cover;}
Old-fashioned Oyster