Add .js file and .css file reference in your aspx page.add under head part.
Example:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="WebApplication1.WebForm1" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
//Drag and drop your js and css file.
<link rel="stylesheet" type="text/css" href="yourcssfilename.css" />
<script type="text/javascript" src="yourjsfilename.js"></script>
</head>
<body>
<form id="form1" runat="server">
<div>
</div>
</form>
</body>
</html>