How to make an inverse transparent circle in CSS [duplicate]

Answer 1

jsBin demo

• Place an overflow:hidden square with no background.
• Inside that square - put a circle with a high box-shadow spread radius

#image{
  position:relative;
  margin:0 auto;
  background: url(http://i.imgur.com/gVcxX9C.png);
  height:500px;
  width:600px;
}
#box{
  position:absolute;
  left:300px;
  top:200px;
  width:200px;
  height:250px;
  overflow:hidden; /* to contain #circle's box-shadow */
}
#circle{
  position:relative;
  margin:30px auto;
  width: 150px;
  height:150px;
  box-shadow: 0 0 0 100px #fff; /* !!! */
  border-radius:50%;
}