Need Scrollable GridView With Fixed Header

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ASP.NET

CSS

i hv designed a gridview with div tag which is scrollabe , but when i scroll the grid its header part is also scrolled. header part should not be scrolled for my requirement.
Plz Provide me idea...
Below is my code......

<div id="divCall" class="div">

<asp:GridView ID="GridCall" runat="server" CssClass="Grid"
        AutoGenerateColumns="false" RowStyle-HorizontalAlign="Justify"
        ShowHeader="true" ShowFooter="false" AllowPaging="false"
        GridLines="Horizontal"
        onselectedindexchanged="GridCall_SelectedIndexChanged" AutoGenerateSelectButton="true">

<HeaderStyle BackColor="AliceBlue" BorderStyle="Double" Height="25px" HorizontalAlign="Center" VerticalAlign="Middle" />
<RowStyle BackColor="Wheat" BorderStyle="Solid" Height="20px" VerticalAlign="Middle" HorizontalAlign="Center"/>
<Columns>
<asp:TemplateField ShowHeader="true" HeaderText="Call ID" >
<ItemTemplate> <asp:TextBox ID="txtCallID" runat="server" CausesValidation="false" ReadOnly="true" CssClass="txt" Text='<%# Bind("complain_no") %>'>&#39;
    &gt;</asp:TextBox></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField ShowHeader="true" HeaderText="P No" >
<ItemTemplate> <asp:TextBox ID="txtPNo" runat="server" CausesValidation="false" ReadOnly="true" CssClass="txt" Text='<%# Bind("pno") %>'></asp:TextBox></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField ShowHeader="true" HeaderText="Suspected Problems" >
<ItemTemplate> <asp:TextBox ID="txtProblem" runat="server" CausesValidation="false"  CssClass="txt" Text='<%# Bind("problem") %>'></asp:TextBox></ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</div>

and CSS code is here....

.div
{
    overflow:scroll;
    width:100%;
    height:300px;
}
.Grid
{
    width:98%;
    height:500px;
}