SOURCE

<div class="main">
  <div class="main-content">
    main content
  </div>
</div>
<div class="left">left</div>
<div class="right">right</div>

* {
  margin: 0;
  padding: 0
}

.main {
  float: left;
  width: 100%;
}
.main .main-content {
  margin: 0 210px;
  background-color: rgba(33, 114, 214, 0.8);
  height: 500px;

}

.left {
  width: 200px;
  float: left;
  background-color: rgba(255, 82, 0, 0.8);
  margin-left: -100%;
  height: 200px;
}

.right {
  width: 200px;
  height: 200px;
  background-color: rgba(90, 243, 151, 0.8);
  float: left;
  margin-left: -200px;
}