Tkinter Scrollbar not working

[GaMoVeHack (GaMo)]

hi and im using python 3.7 tkinter to coding notepad.

the scroll bar is not working properly
can anyone fix that?
thanks for the answer.

import os
from tkinter import *
from tkinter import filedialog, colorchooser, font
from tkinter.messagebox import *
from tkinter.filedialog import *
import logging


def change_color():
    color = colorchooser.askcolor(title="Change color to...")
    text_area.config(fg=color[1])



def new_file():
    window.title("Untitled")
    text_area.delete(1.0, END)


def open_file():
    file = askopenfilename(defaultextension=".txt",
                           file=[("All Files", "*.*"),
                                 ("Text Documents", "*.txt")])

    if file is None:
        return

    else:
        try:
            window.title(os.path.basename(file) + " - FlexPad")
            text_area.delete(1.0, END)

            file = open(file, "r")

            text_area.insert(1.0, file.read())

        except Exception:
            window.title("FlexPad v1.0")

        finally:
            file.close()


def save_file():
    file = filedialog.asksaveasfilename(initialfile='*.txt',
                                        defaultextension=".txt",
                                        filetypes=[("All Files", "*.*"),
                                                   ("Text Documents", "*.txt")])

    if file is None:
        return

    else:
        try:
            window.title(os.path.basename(file))
            file = open(file, "w")

            file.write(text_area.get(1.0, END))

        except Exception:
            print("couldn't save file")

        finally:
            file.close()


def cut():
    text_area.event_generate("<<Cut>>")


def copy():
    text_area.event_generate("<<Copy>>")

def paste():
    text_area.event_generate("<<Paste>>")


def about():
    showinfo("About this program", "TextEditor Version 1.0")
def help():
    showinfo("Help", "Coming Soon!")


def quit():
    window.destroy()


window = Tk()
window.title("TextEditor v1.0")
file = None

window_width = 500
window_height = 500
screen_width = window.winfo_screenwidth()
screen_height = window.winfo_screenheight()

x = int((screen_width / 2) - (window_width / 2))
y = int((screen_height / 2) - (window_height / 2))

window.geometry("{}x{}+{}+{}".format(window_width, window_height, x, y))

font_name = StringVar(window)
font_name.set("Times New Roman")

font_size = StringVar(window)
font_size.set("13")

text_area = Text(window, font=(font_name.get(), font_size.get()))

scroll_bar = Scrollbar(text_area)
window.grid_rowconfigure(0, weight=1)
window.grid_columnconfigure(0, weight=1)
text_area.grid(sticky=N + E + S + W)
scroll_bar.pack(side=RIGHT, fill=Y)
text_area.config(yscrollcommand=scroll_bar.set)


menu_bar = Menu(window)
window.config(menu=menu_bar)

file_menu = Menu(menu_bar, tearoff=0)
menu_bar.add_cascade(label="File", menu=file_menu)
file_menu.add_command(label="New", command=new_file)
file_menu.add_command(label="Open", command=open_file)
file_menu.add_command(label="Save", command=save_file)
file_menu.add_separator()
file_menu.add_command(label="Exit", command=quit)

edit_menu = Menu(menu_bar, tearoff=0)
menu_bar.add_cascade(label="Edit", menu=edit_menu)
edit_menu.add_command(label="Cut", command=cut)
edit_menu.add_command(label="Copy", command=copy)
edit_menu.add_command(label="Paste", command=paste)
edit_menu.add_command(label="Change Color", command=change_color)

help_menu = Menu(menu_bar, tearoff=0)
menu_bar.add_cascade(label="Help", menu=help_menu)
help_menu.add_command(label="Help", command=help)
help_menu.add_command(label="About", command=about)

window.mainloop()