SOURCE

<div class="box">
  <div class="center">
    <div class="center_in"></div>
  </div>
  <div class="left"></div>
  <div class="right"></div>
</div>

.box{
  width:500px;
  height:300px;
  background:red;
}

.center{
  width:100%;
  height:100%;
  background:blue;
  float:left;
}
.center_in{
    height:100%;
    background:yellow;
    margin:0 100px;
}
.left,.right{
  width:100px;
  background:pink;
  height:100%;
  float:left;
}

.left{
  margin-left:-100%;
}
.right{
  margin-left: -100px;;
}