problem with replacing textarea

I can't replace the original textarea with the ckeditor. This is my code:
I'm using ASP.Net

<form id="formtesting" runat="server">  
<p>  
    <textarea id="editor1" name="editor1" cols="20" rows="2"></textarea>
    
    <script type="text/javascript">
        CKEDITOR.replace('editor1',
    {
        toolbar: 'Basic',
        uiColor: '#9AB8F3'
    });
    </script>
</p>  
<p>
    <asp:Button ID="Button1" runat="server" Text="Button" /> 
</p>  
</form>