pygame surface.fill() does not work well

import sys
import pygame
from pygame.locals import QUIT

# globals
WINDOW_SIZE= (400,300)
WINDOW_TITLE="Pygame Count"

defmain():
    pygame.init()
    surface=pygame.display.set_mode (WINDOW_SIZE)
    pygame.display.set_caption(WINDOW_TITLE)
    sysfont=pygame.font.SysFont(None,36)
    counter = 0
    while True:
        for event in pygame.event.get():
            if event.type==QUIT:
                pygame.quit()
                sys.exit()
        counter+=1
        surface.fill((255,255,255))#=>Change this number to change the background color.
        count_image=sysfont.render(
            "count is {0}".format(counter), True, (0, 0, 0))#=>The character color changes as well.
        Surface.blit(count_image, (64,64))#=> Inserted to draw characters.
        pygame.display.update()
        Inserted a delay of time to see that the pygame.time.delay(100)#=> counter has changed.

if__name__=="__main__":
    main()