如何设置浏览器滚动条来滚动页面的一部分？（高于隐藏的页脚部分）就像http://i-donline.com/
.header{
position: fixed;
left: 0;
top: 0;
width: 1000px;
height: 100px;
background: blue;
z-index: 1;
}
.contentwrap{
position: absolute;
left: 0;
top: 100px;
width: 1000px;
height: 250px;
background: ;
}
.footer{
position: fixed;
left: 0;
top: 350px;
width: 1000px;
height: 300px;
background: blue;
}
.row{
position: relative;
left: 0;
top: 0;
width: 800px;
height: 250px;
border: purple 1px solid;
background: gray;
}