Pygame不会绘制或填充屏幕

import pygame

pygame.init()
screen = pygame.display.set_mode((800, 600))

import pygame

pygame.init()
screen = pygame.display.set_mode((800, 600))

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    
    # 绘制或填充屏幕的代码放置在这里
    
    pygame.display.flip()

import pygame

pygame.init()
screen = pygame.display.set_mode((800, 600))

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    
    # 绘制一个红色矩形
    pygame.draw.rect(screen, (255, 0, 0), pygame.Rect(100, 100, 200, 200))
    
    pygame.display.flip()