html底部div固定在底部

整体结构：

保险购买

    

        

        
我的账户
        
    
    样式描述：
    .footer_div_outer{
width: 100%;height:45px;
 _position:absolute;
z-index:999; position:fixed; bottom:0; left:0;
 _top: expression_r(documentElement.scrollTop + documentElement.clientHeight-this.offsetHeight); 
 overflow:visible;

}

.footer_div{
width:50%;height:45px;
float: left;
background-image: url(../img/all_purchase_down.png);
}
.footer_div2{
width:50%;height:45px;
float: right;
background-image:url(../img/all_account_down.png);
}

footer_text{

font-size: 14px;
font-weight: bold;
color: white;
text-align: center;
line-height: 70px;

}