why the pygame.draw.rect() does not work? i want to creat an effect, when mouse moves over a button, just draw a frame around the button. i have a try, but it seemed something wrong? why?
here is my code

    import pygame

    BUTTON = pygame.Rect(100,100,100,100)
    pygame.init()
    screen = pygame.display.set_mode((640,480))
    done = False
    while not done:
        screen.fill((255,255,255))
        pygame.draw.rect(screen,(0,0,255),(110,110,80,80))
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                done = True
            x,y = pygame.mouse.get_pos()
            if BUTTON.collidepoint(x,y):
                pygame.draw.rect(screen,(0,0,0),BUTTON,3)
        pygame.display.update()
    pygame.quit()
