三列，左右两列宽度固定，中间宽度自适应

body{
margin:0;
}
#wrapper{
height: 300px;
overflow: hidden;
}
.left{
width: 200px;
height: 100%;
background: red;
float: left;
}
.right{
width: 200px;
height: 100%;
float: right;
background: green;

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