Jahliah 0 Light Poster

I want to set value for html input text through code behind but can't seem to work :(
p.s. i'm new to c# and this is my first c# project. I appreciate any type of help or critic.
Thanks!

Error in banana.cs: "txt_URL" is not in context

apple.html:

<%@ Page Language="C#"
AutoEventWireup="true".
         src="banana.cs"
         inherits="BananaPage.banana"
%>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
</head>
<body>
        <input id="txt_URL" type="text" name="txt_URL" runat="server"/>
</body>
</html>

banana.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Text;
using System.Data;

namespace BananaPage
{
   public partial class banana : Page

    {
        //Declare controls used
        protected System.Web.UI.HtmlControls.HtmlInputText txt_URL;

        protected void Page_Load(object sender, EventArgs e)
        {
      txt_URL.Value = "test";
        }
    }
}