SOURCE

<div id="main">
  <div id="left">1</div>
  <div id="right">3</div>
  <div id="center">2</div>
</div>

#main {
  height: 200px;
  width: 100%;
}

* {
  margin: 0;
  padding: 0;
  text-align: center;
  font-size: 50px;
}

#left, #right {
  background-color: red;
  height: 100%;
  width: 200px;
}

#left {
  float: left;
}

#center {
  height: 100%;
  background-color: #e1e1e1;
  margin: 0 200px;
}

#right {
  float: right;
  background-color: orange;
}