SOURCE

<div id="wrap">
  <div class="center">  
<div class="inner"></div>
  </div>
<div class="left"></div>
<div class="right"></div>
</div>

html,body{
    height: 100%;
    overflow: hidden;
}

#wrap{
    height: 100%;
}

.left,.right{
    width:200px;
    height: 200px;
    background: pink;
    float: left;
}

.center{
    width: 100%;
    float: left;
    
}

.center .inner{
    min-height: 200px;
    background: gray;
    margin: 0 200px;
}

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

.right{
    margin-left:-200px;
   
}