after updatepanel.update, the style of the checkbox will be removed

How can I fix this problem? When updatepanel.update, the checkbox or radiobutton style will disappear my hmtl:

<asp:ScriptManager ID="ScriptManager1" runat="server" EnableScriptGlobalization="True" EnableCdn="True"></asp:ScriptManager>

<asp:UpdatePanel ID="upnl_1" runat="server">
    <ContentTemplate>
       <asp:DropDownList ID="ProjectsList_ddl" runat="server" AutoPostBack="true"
                             OnSelectedIndexChanged="ProjectsList_ddl_SelectedIndexChanged">
       </asp:DropDownList>                                              
    </ContentTemplate>

<asp:UpdatePanel ID="upnl_2" runat="server">
 <ContentTemplate>
       <asp:Repeater ID="toolsList_rpt" runat="server">
          <ItemTemplate>
              <input id="myradio" runat="server" type="radio" name="drone" class="flat">
                     <span><%#Eval("Title")%></span>   
          </ItemTemplate>
       </asp:Repeater>                                                           
     <asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="upnl_1" DisplayAfter="0">
    <ProgressTemplate>                                                      
     <asp:Image ID="img" runat="server" ImageUrl="/loader.gif"  />                                                         
    </ProgressTemplate>
   </asp:UpdateProgress>
  </ContentTemplate>

before load data (updatepanel.update & toolsList_rpt.bind)

after thanks everyone