Максим Люмен

<div class="wrapper"> 
  <section></section>
</div>

html,body{
  background:#ddd;
}
.wrapper{
  width:500px;
  height:200px;
  background:#fff;
  margin:30px auto;
  position:relative;
}
section{
  width:460px;
  height:160px;
  background:#fff;
  position:absolute;
  top:50%;
  left:50%;
  margin-top:-80px;
  margin-left:-230px;
  border:2px solid #ddd;
}
section:after{
  content:"";
  display:block;
  width:30px;
  height:30px;
  background:#fff;
  position:absolute;
  bottom:-15px; left:50%;
  margin-left:-10px;
  border:1px solid #ddd;
}
section:before{
  content:"";
  display:block;
  width:30px;
  height:30px;
  background:#fff;
  position:absolute;
  top:-15px; left:50%;
  margin-left:-10px;
  border:1px solid #ddd;
}