SOURCE

<div class="relative">
  <div class="absolute1"></div>
  <div class="absolute2"></div>
</div>

.relative {
  position:relative;
  border:1px solid blue;
  width:100px;
  height:100px;
}
.absolute1{
  position:absolute;
  top:0;
  left:0;
  width:50px;
  height:50px;
  border:1px solid red;
}

.absolute2{
  position:absolute;
  top:0;
  left:0;
  width:70px;
  height:70px;
  border:1px solid green;
}