Update Panel asp.net

<asp:Button ID="btnGetContinentCountryFrom"
    runat="server" Text="Get Country & Continent!"
    OnClick="btnGetContinentCountryFrom_Click"
    CssClass="input-hidden"
     />                               
<asp:TextBox ID="txtPortFromDetail" CssClass="input-width2" placeholder="Detail" runat="server" ReadOnly="false" />

<asp:UpdatePanel ID="updatePanelPortFrom" runat="server">
    <ContentTemplate>
        <asp:TextBox ID="txtPortFromContinental" CssClass="input-width2 input-disabled" placeholder="Continental" runat="server" ReadOnly="true" />
        <asp:HiddenField ID="hdnPortFromContinent" runat="server" />
    
        <asp:TextBox ID="txtPortFromCountry" CssClass="input-width2 input-disabled" placeholder="Country" runat="server" ReadOnly="true" />
        <asp:HiddenField ID="hdnPortFromCountry" runat="server" />                                    
    </ContentTemplate>
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="btnGetContinentCountryFrom" EventName="Click" />
    </Triggers>
</asp:UpdatePanel>