SOURCE

<header><h4>Header内容区</h4></header>
<div class="container">
  <div class="middle"><h4>中间弹性区</h4></div> 
  <div class="left"><h4>左边栏</h4></div> 
  <div class="right"><h4>右边栏</h4></div>
</div>
<footer><h4>Footer内容区</h4></footer>

header{width: 100%;height: 40px;background-color: darkseagreen;}
footer{width: 100%; height: 30px;background-color: darkslategray;}

.container{ 
  height:200px;overflow:hidden;
  padding: 0 100px;
}
.middle{
  width: 100%;height: 200px; 
  background-color: deeppink;  float:left;
}
.left{ 
  width: 100px;height: 200px;
  background-color: blue;
  float:left;
  margin-left:-100%;
  position: relative; 
  left: -100px;

}
.right{
  width: 100px;height: 200px;  
  background-color: darkorchid;
  float:left;
  margin-left:-100px;
  position: relative; right: -100px;
}