CSS expressions do not work i n IE11

I have a Datagrid in my app , its running in IE11. I know these CSS expression are no longer supported in IE11. If you could see the below CSS class, it has top expression which is not working in IE 11. And whenever I use vertical scroll bar to see all the records in my grid, Datagrid header also moves up, it doesnt stay fixed. I have no idea how can I remediate this top expression. If any of you have come across these DataGrid header issues in IE11 , Please write back to me. Thanks in advance.

.DataGridFooter
{
position: relative;
top: expression(this.offsetParent.scrolltop - 20 );
background-color: Gainsboro;
vertical-align: bottom;
margin-bottom: 2px;
font-weight: bold;
}