SOURCE

<div class="container">
  <div class="main">main</div>
  <div class="left">left</div>
  <div class="right">right</div>
</div>

* {
  padding: 0;
  margin: 0;
}
.container {
  margin-left: 100px;
  margin-right: 100px;
}
.main {
  width: 100%;
  float: left;
  background-color: yellow;
}
.left {
  width: 100px;
  margin-left: -100%;
  float: left;
  position: relative;
  left: -100px;
  background-color: orange;
}
.right {
  width: 100px;
  margin-right: -100px;
  float: left;
  position: relative;
  background-color: red;
}