update-panel.aspx

<asp:ScriptManager ID="ScriptManager1" runat="server" />
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
  <ContentTemplate>
    <asp:Calendar ID="Calendar1" ShowTitle="True" OnSelectionChanged="Calendar1_SelectionChanged"
      runat="server" />
    <div> Background: <br />
      <asp:DropDownList ID="ColorList" AutoPostBack="True" OnSelectedIndexChanged="DropDownSelection_Change"
        runat="server">
        <asp:ListItem Selected="True" Value="White"> White </asp:ListItem>
        <asp:ListItem Value="Silver"> Silver </asp:ListItem>
        <asp:ListItem Value="DarkGray"> Dark Gray </asp:ListItem>
        <asp:ListItem Value="Khaki"> Khaki </asp:ListItem>
        <asp:ListItem Value="DarkKhaki"> Dark Khaki </asp:ListItem>
      </asp:DropDownList>
    </div> Selected date: <asp:Label ID="SelectedDate" runat="server">None.</asp:Label>
  </ContentTemplate>
</asp:UpdatePanel>