Как сделать чтобы функция закрывалась?

from tkinter import *
from tkinter import Tk, Menu, filedialog, messagebox, LabelFrame, RIDGE, \
Frame, Entry, W, END, Button, E, Label, Listbox, Scrollbar, \
RIGHT, Y, X, BOTTOM, LEFT
from math import *
import time
global x1
global y1
global l1
global font
font = 5
y1=270
x1=250
 
def RIGHT():
global x1
x2=x1
x2=x2+font
x1=x2
l1.place(x = x2, y = y1)
def LEFT():
global x1
x2=x1
x2=x2-font
x1=x2
l1.place(x = x2, y = y1)
def DOWN():
global y1
y2=y1
y2=y2+font
y1=y2
l1.place(x = x1, y = y2)
def UP():
global y1
y2=y1
y2=y2-font
y1=y2
l1.place(x = x1, y = y2)
def close():
root.quit()
root = Tk()
root['bg'] = 'black'
root.title("Выполнил студент группы 18-ЗИЭ-1")
lbox = Listbox(width=10, height=5)
lbox.place(x = 5, y = 0)
for i in ('5', '10', '15', '20'):
lbox.insert(END, i)
def Opr(event):
global l1
global font
if lbox.get(lbox.curselection())=='5':
font = 5
if lbox.get(lbox.curselection())=='10':
font = 10
if lbox.get(lbox.curselection())=='15':
font = 15
if lbox.get(lbox.curselection())=='20':
font = 20
b =Button(fg = "#555", bg = "#ffffff", text = 'x', font=("Comic Sans MS", 10, "bold"))
b.place(x = 100, y = 0)
b1 =Button(fg = "#555", bg = "#ffffff", text = 'Close', font=("Comic Sans MS", 10, "bold"),command = root.destroy)
b1.place(x = 100, y = 35)
b.bind('<Button-1>', Opr)
 
w = root.winfo_screenwidth() # Ширина
h = root.winfo_screenheight() # Длина
w = w//3
h = h//3
w = w - 300
h = h - 300
root.geometry('600x600+{}+{}'.format(w, h))
Button(text="Вниз", background="#555", foreground="#ccc",padx="15", pady="6", font="15",command = DOWN).pack(side = 'bottom'
)
Button(text="Вправо", background="#555", foreground="#ccc",padx="15", pady="6", font="15",command = RIGHT).pack(side = 'right')
Button(text="Влево", background="#555", foreground="#ccc",padx="15", pady="6", font="15",command = LEFT).pack(side = 'left')
Button(text="Вверх", background="#555", foreground="#ccc", font="15",command = UP).pack(side = 'top')
l1 = Label(text="Mr.Robot", font='MrRobot 16',compound="center", bg='red')
l1.place(x = x1, y = y1)
print(x1)
root.mainloop()