[Python] tkinter progress bar freezes in I do anything else

I built a simple progress bar (I want to use it in many other programs), but the problem is, if I move the window, or click on anything else the progress window freezes. The script keeps running but the progress window has "Not Responding" and does not update.

from tkinter import *
from tkinter.ttk import *
from datetime import *
import time

def main():
# get start time to calc execution time
start_time = datetime.now().replace(microsecond=0)
print(start_time, "\n")

GB = 100
window = Tk()
percent = StringVar()
text = StringVar()
fleft = StringVar()
download = 0
speed = 5

percentLabel = Label(window, textvariable=percent).pack()
taskLabel = Label(window, textvariable=text).pack()
leftLabel = Label(window, textvariable=fleft).pack()


bar = Progressbar(window,orient=HORIZONTAL,length = 300)
bar.pack(pady=10)


while (download < GB):
download += speed
time.sleep(1)
bar['value']+=(speed/GB)*100
percent.set(str(int((download/GB)*100))+"%")
text.set(str(download)+" files completed!")
fleft.set(str(int(GB - download)) + " left to complete.")
window.update_idletasks()
window.mainloop()

if __name__ == '__main__':
main()

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