Yes, that works, but this does not:
<%@ Page Language="c#" %>
<%@ Register Namespace="CuteWebUI" Assembly="CuteWebUI.AjaxUploader" TagPrefix="CuteWebUI" %>
<html>
<head>
<style>
.redColor {
background-color: blue;
}
</style>
</head>
<body>
<form id="Form1" method="post" runat="server">
<CuteWebUI:UploadAttachments ID="uploader1" runat="server"
ProgressCtrlID="progress"
CancelButtonStyle-CssClass="redColor"></CuteWebUI:UploadAttachments>
<div id="progress">
Progress bar follows
</div>
</form>
</body>
</html>