or

<fieldset> <legend>Refresh Settings</legend> <table> <tr> <td class="AutoRefreshEnabled"> Auto-Refresh Enabled:</td> <td class="AutoRefreshCheckbox"> <asp:CheckBox ID="CheckBox1" runat="server" AutoPostBack="True" oncheckedchanged="CheckBox1_CheckedChanged" /> </td> <td class="AutoRefreshNumericTextbox"> <telerik:RadNumericTextBox ID="RadNumericTextBox1" Runat="server" Label="Auto-Refresh Interval:" MaxValue="60" MinValue="0" ShowSpinButtons="True" Value="0" Width="175px" Enabled="False" LabelCssClass="riLabel LabelDisabled"> <NumberFormat DecimalDigits="0" /> </telerik:RadNumericTextBox> </td> </tr> </table></fieldset>protected void CheckBox1_CheckedChanged(object sender, EventArgs e){ RadNumericTextBox1.Enabled = (sender as CheckBox).Checked; if (RadNumericTextBox1.Enabled) { RadNumericTextBox1.LabelCssClass = "LabelEnabled"; } else { RadNumericTextBox1.LabelCssClass = "LabelDisabled"; }}.LabelEnabled{ color: Black !important;}.LabelDisabled{ color: Gray !important;}<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server"> <AjaxSettings> <telerik:AjaxSetting AjaxControlID="CheckBox1"> <UpdatedControls> <telerik:AjaxUpdatedControl ControlID="RadNumericTextBox1" /> </UpdatedControls> </telerik:AjaxSetting></telerik:RadAjaxManager>