SOURCE

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

.container {
  padding: 0 300px 0 200px;
  background-color: pink;
}

.main,
.left,
.right {
  position: relative;
  float: left;
  min-height: 100px;
}

.main {
  width: 100%;
  background-color: red;
}

.left {
  width: 200px;
  left: -200px;
  margin-left: -100%;
  background-color: green;
}

.right {
  right: -300px;
  margin-left: -300px;
  width: 300px;
  background-color: yellow;
}