How to get image info from css into MasterPage'gridview?

i try to givee style via GridView.css into Masterpage my masterpage includes 3 pages also 3 pages sources has GridView. i added head tags css file:

<link type="text/css" href="../CSS/GridView.css" rel="stylesheet" />
also give property my GridVew source:

  <asp:GridView ID="gwRehber" runat="server" AutoGenerateColumns="false" CssClass="tablestyle" 
           onrowcommand="gwRehber_RowCommand">
            <AlternatingRowStyle CssClass="altrowstyle" />
                        <HeaderStyle CssClass="headerstyle" />
                        <RowStyle CssClass="rowstyle" />
       <Columns>
       <asp:TemplateField>
       <ItemTemplate>
        <asp:Button runat="server" ID="btnID" CommandName="select"  CommandArgument='<%# Eval("ID") %>'  Text="Seç" />
       </ItemTemplate>

       </asp:TemplateField>
          <asp:BoundField DataField="Ad" HeaderText="Ad"  Visible="true"  />
       <asp:BoundField DataField="BireyID" HeaderText="BireyID" Visible="false" />
       <asp:BoundField DataField="Degistiren" HeaderText="Değiştiren" Visible="false" />
        <asp:BoundField DataField="EklemeTarihi" HeaderText="EklemeTarihi" Visible="true" />
       <asp:BoundField DataField="DegistirmeTarihi" HeaderText="Değiştirme Tarihi"  Visible="true" />
       <asp:BoundField DataField="Ekleyen" HeaderText="Ekleyen" Visible="true" />
        <asp:BoundField DataField="ID" HeaderText="ID" Visible="false" />
       <asp:BoundField DataField="Imza" HeaderText="Imza" Visible="true" />
        <asp:BoundField DataField="KurumID" HeaderText="KurumID" Visible="false" />
       </Columns>
       </asp:GridView>/code>