Async Post Back - Lost Javascript and CSS after Async Post Back

Hello Community,

i have the following problem. I would like to fire an asyncpostback after the text changed in a textfield.

The problem is, that i've styled my site with some css and JavaScript functions. After the Async Postback i lost some functionalities and CSS formating.  Can anybody help me with this problem? Here is my source code:

C# Class:

protected void txt_PartNr_TextChanged(object sender, EventArgs e)
{
            txt_PartNr.Attributes.Add("class", "red");
}

ASPX Site:

<asp:Content ID="ContentMain" ContentPlaceHolderID="MainContent" runat="server"><asp:UpdatePanel runat="server" ID="MainContentUpdatePanel" UpdateMode="Always"><ContentTemplate><div id="spaceContent"><div class="row hide-on-med-and-down"><div><label>&nbsp;</label></div></div></div><!-- Autogenerate new Claim Nr and fills it --><div class="row card " style="margin-left: 5%;"><div class="row"><div class="input-field col s12 sickSignsOrange big"><asp:Literal runat="server" ID="ltlReclaimNr" /></div></div><div class="row"><!--PartNr --><div class="input-field col s3 offset-s1"><asp:TextBox runat="server" ID="txt_PartNr" AutoPostBack="true"/><label for="idPartNr"><asp:Literal runat="server" Text="<%$Resources:sick.language, partNr%>" /></label></div>                   </div>    </div></ContentTemplate><Triggers><asp:AsyncPostBackTrigger ControlID="txt_PartNr" EventName="TextChanged"/></Triggers></asp:UpdatePanel></asp:Content>

The Event works fine, but the problem is after the Event some other functions doesn't work (JavaScript and CSS Formats for Selections / Combobox).

Thanks for your help.