<td class="style2"  
                style="background-color: #ECFFF1; text-align: center; "  
                valign="top"> 
                <br /> 
                <asp:Button ID="Button1" runat="server" Text="Button"  
                    onclick="Button1_Click" PostBackUrl="~/calendar.aspx" /> 
            </td> 
            <td class="style3"> 
                 
 
                <div id="box"> 
                    <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"> 
                        <ContentTemplate> 
                            <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server"> 
                            </asp:ContentPlaceHolder> 
                        </ContentTemplate> 
                        <Triggers> 
                          <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" /> 
                        </Triggers> 
                    </asp:UpdatePanel> 
                </div> 
 
 
 
            </td>