Then add this script into head section and show the effect.
<style id="cssStyle" type="text/css" media="all">
.CS
{
background-color:#abcdef;
color: Yellow;
border: 1px solid #AB00CC;
font: Verdana 10px;
padding: 1px 4px;
font-family: Palatino Linotype, Arial, Helvetica, sans-serif;

}
</style>

And
<asp:FileUpload ID="FileUpload1" CssClass="CS" runat="server" />
Or
html file upload
<input id="readFile" type="file" class="CS" runat="server" />