Centering and adding a push button to a grid window, TKinter

[Edward_]

This May be really simple, but I'm not finding enough details to help as I'm just learning TKinter.

I have a simple grid sourced by a Python list, and I'm trying to center it regardless of window size, and add single push button at bottom of the window.
What I have tested caused the full window to grey out.

my code:

import tkinter as tk
from tkinter import *
import tkinter.font as font
window = tk.Tk()
window.title("Feed Bins")
window.geometry("800x400")

aList = ["Bin 1", "Bin 2", "Bin 3", "Bin 4", "Bin 5","Bin 6", "Bin 7", "Bin 8", "Bin 9", "Bin 10", "Bin 11",
        "Bin 12", "Bin 13", "Bin 14", "Bin 15"]
onList = ["Bin 3", "Bin 12", "Bin 14"] # For testing, usually empty

myFont2 = font.Font(size=10)

label= [0] * 15
for x in range(5):    # Number of Rows
   for y in range(3): #Number of Colums
       frame = tk.Frame(master=window,relief=tk.RAISED,borderwidth=4)
       frame.grid(row=x, column=y, padx=5, pady=5)  # line 13
       label[x+(y*5)] = tk.Label(master=frame, text=aList[x+(y*5)],font=myFont2, height=3, width=20)
       label[x+(y*5)].pack(fill="x")

def check_alerts():
   global aList,onList
   for x in range(0,len(aList)):
       if aList[x] in onList:
           label[x].config(bg = "red")
       else:
           label[x].config(bg = "lightgrey")
   window.after(1000,check_alerts)
   
check_alerts()

window.mainloop()   

Any assistance greatly appreciated.