from tkinter import *
from tkinter.ttk import *
from time import strftime

root = Tk()
root.title("Relógio")

def relogio():
    horario = strftime("%H:%M:%S")
    label.config(text=horario)
    label.after(1000, relogio)

label = Label(root, font=("Helvetica", 60), background="#000", foreground = "#00FF04")
label.pack(anchor = "center")

relogio()

mainloop()