css 两边宽度固定中间自适应宽度

#content_left{   //左
73px;
height:100px;
vertical-align:middle;
margin-right:-100px;
float:left;
background-color:#FFFF99;
}
#content_right{  //右
73px;
height:100px;
vertical-align:middle;
margin-left:-100px;
float:right;
background-color:#FFFF99;
}
#content_middle{  //中
auto;
height:100px;
margin:0 100px;
background-color:#0057B9;
text-align:center;
}