RequiredFieldValidator for asp dropdownlist (C#)

<%@ Page Language="C#" %>

<script runat="server">

    void btnSubmit_Click(Object sender, EventArgs e)
    {
        if (Page.IsValid)
            lblResult.Text = dropFavoriteColor.SelectedValue;
    }
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Show Initial Value</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    <asp:Label
        id="lblFavoriteColor"
        Text="Favorite Color:"
        AssociatedControlID="dropFavoriteColor"
        Runat="server" />
    <br />
    <asp:DropDownList
        id="dropFavoriteColor"
        Runat="server">
        <asp:ListItem Text="Select Color" Value="none" />
        <asp:ListItem Text="Red" Value="Red" />    
        <asp:ListItem Text="Blue" Value="Blue" />    
        <asp:ListItem Text="Green" Value="Green" />    
    </asp:DropDownList>
    <asp:RequiredFieldValidator
        id="reqFavoriteColor"
        Text="(Required)"
        InitialValue="none"
        ControlToValidate="dropFavoriteColor"
        Runat="server" />
        
    <br /><br />
    
    <asp:Button
        id="btnSubmit"
        Text="Submit"
        Runat="server" OnClick="btnSubmit_Click" />
    
    <hr />
    
    <asp:Label
        id="lblResult"
        Runat="server" />
    
    </div>
    </form>
</body>
</html>

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