Dropdown style broken inside UpdatePanel

I have 2 dropdownlist within the updatepanel when I select a item from dropdownlist another list change according to another ddl. But that's time I lost my style of dropdownlist

This is my aspx code

<asp:UpdatePanel runat="server" ID="pnlModalFirst" UpdateMode="Conditional"><ContentTemplate><div class="modal-body"><asp:DropDownList runat="server" CssClass="selectpicker markaselect margin-bottom-10" ID="ddlBrand" ClientIDMode="Static" DataValueField="Id" DataTextField="BrandName" AutoPostBack="True" OnSelectedIndexChanged="ddlBrand_SelectedIndexChanged" title="Marka Seçiniz" data-live-search="true" /><asp:DropDownList runat="server" CssClass="selectpicker modelselect margin-bottom-10" ID="ddlModel" ClientIDMode="Static" AutoPostBack="True" OnSelectedIndexChanged="ddlModel_SelectedIndexChanged" title='Model Seçiniz' /><asp:DropDownList runat="server" CssClass="hidden selectpicker margin-bottom-10" ID="ddlKaroser" title='Karoser Seçiniz' /><asp:Button runat="server" CssClass="col-md-2 btn-block btn-u btn-u-blue btn-u-lg " ID="btnDKnow" Text="Teklifleri Al" OnClick="btnDKnow_Click" ValidationGroup="modalKnow" /></div></ContentTemplate><Triggers><asp:AsyncPostBackTrigger ControlID="ddlBrand" EventName="SelectedIndexChanged" /><asp:AsyncPostBackTrigger ControlID="ddlModel" EventName="SelectedIndexChanged" /></Triggers></asp:UpdatePanel>

And also I use [this] plugin my dropdownlist but when I change first ddl all style broken like this

Before select ddl

After select ddl