<div class="container">
  <div class="left"></div>
  <div class="right"></div>
  <div class="main"></div>
</div>
* {
  margin: 0;
  padding: 0;
}
.left {
  float: left;
  width: 100px;
  height: 200px;
  background: red;
}

.right {
  float: right;
  width: 200px;
  height: 200px;
  background: green;
}

.main {
  height: 200px;
  margin-left: 100px;
  margin-right: 200px;
  background: blue;
}

External CSS

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External JavaScript

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