java script not work with master page

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ASP.NET

i have a master page which have java script for style a div class:

<script type="text/javascript">
    $(document).ready(function () {

        var options = {
            styleClass: "selectDark",
            jScrollPane: 1
        }

        $(".mySelect").styleSelect(options);

    });
</script>

in next step i also have a page:
which have drop down:

<asp:DropDownList ID="DropDownList2"  CssClass="mySelect" runat="server">
        <asp:ListItem>1</asp:ListItem>
        <asp:ListItem>2</asp:ListItem>
    </asp:DropDownList>

but this "mySelect" class not work with this,

1. it work well if i not use master page, and only have a simple page:
2. it work with master page if i use html drop down like this:

<select id="Select1" class="mySelect">
       <option>1</option>

         <option>2</option>
   </select>

so what can i do, i also put this java script in content page, or master page but it not work when master page is use and asp.net control is used,
some one says that control id is changed with master page,
but here is a div class, and how this div class id changed.
plz help me