Edit in JSFiddle

<div class="box blue"></div>
<div class="box red"></div>
<div class="box green"></div>

.box{ 
    height: 60px; 
    width:60px;
    margin: 5px 0;
 }
 
 .blue{
   border: 1px solid blue;
   background-color: #74d;
  
}
.green{
   border: 1px solid red;
   position:absolute;
   top:30px;
   left:30px;
   background-color:#145;
   z-index:-1;
}
.red {
   border: 1px solid red;
   width:60px;
}