pygame showing a blue block

blue-block.py

import pygame

pygame.init()

game_width = 640
game_height = 480

screen = pygame.display.set_mode((game_width, game_height)) # size must be (tuple)
pygame.display.set_caption('hello pygame')

# colours
black = (0, 0, 0)
blue = (0, 128, 255)

# box properties
box_width = 50
box_height = 50
box_left = 30
box_top = 30
box_colour = blue

done = False

while not done:

    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        done = True

    screen.fill(black)
    pygame.draw.rect(screen, box_colour, pygame.Rect(box_left, box_top, box_width, box_height))

    pygame.display.flip()