运行效果：

完整源码：

##import library
from tkinter import *
import time
from playsound import playsound


## display window 
root = Tk()
root.geometry('400x300')
root.resizable(0,0)
root.config(bg ='blanched almond')
root.title('TechVidvan - Countdown Clock And Timer')
Label(root, text = 'Countdown Clock and Timer' , font = 'arial 20 bold', bg ='papaya whip').pack()


#display current time#######################

Label(root, font ='arial 15 bold', text = 'current time :', bg = 'papaya whip').place(x = 40 ,y = 70)


####fun to display current time
def clock():
 clock_time = time.strftime('%H:%M:%S %p')
 curr_time.config(text = clock_time)
 curr_time.after(1000,clock)

curr_time =Label(root, font ='arial 15 bold', text = '', fg = 'gray25' ,bg ='papaya whip')
curr_time.place(x = 190 , y = 70)
clock()


#######################timer countdown##########


#storing seconds
sec = StringVar()
Entry(root, textvariable = sec, width = 2, font = 'arial 12').place(x=250, y=155)
sec.set('00')

#storing minutes
mins= StringVar()
Entry(root, textvariable = mins, width =2, font = 'arial 12').place(x=225, y=155)
mins.set('00')


# storing hours
hrs= StringVar()
Entry(root, textvariable = hrs, width =2, font = 'arial 12').place(x=200, y=155)
hrs.set('00')

##########fun to start countdown

def countdown():
 times = int(hrs.get())*3600+ int(mins.get())*60 + int(sec.get())
 while times > -1:
  minute,second = (times // 60 , times % 60)
  
  hour = 0
  if minute > 60:
   hour , minute = (minute // 60 , minute % 60)
   
  sec.set(second)
  mins.set(minute)
  hrs.set(hour)
  
  root.update()
  time.sleep(1)

  if(times == 0):
   playsound('Loud_Alarm_Clock_Buzzer.mp3')
   sec.set('00')
   mins.set('00')
   hrs.set('00')
  times -= 1

Label(root, font ='arial 15 bold', text = 'set the time', bg ='papaya whip').place(x = 40 ,y = 150)

Button(root, text='START', bd ='5', command = countdown, bg = 'antique white', font = 'arial 10 bold').place(x=150, y=210)
  


root.mainloop()