SOURCE

<div class="contioner">
  <div class="left">left</div>
  <div class="right">right</div>
  </div>

.contioner{
  border:1px red solid;
  padding:0px 100px;
}

.left{
  border:1px blue solid;
  float:left;
  width:100px;
  margin-left:-100%;
  left:-100px;
  position:relative;
}
.right{
  border:1px yellow solid;
  float:left;
  width:100px;
}