почему при запуске выводится только чёрный экран?

import pygame
import random
import copy

pygame.init()

I_max = 11
J_max = 21

screen_x = 300
screen_y = 600

screen = pygame.display.set_mode((screen_x, screen_y))
clock = pygame.time.Clock()

pygame.display.set_caption("Tetris Pixel Game")

dx = screen_x/(I_max - 1)
dy = screen_y/(J_max - 1)

fps = 60
grid = []


for i in range(0, I_max):
 grid.append([])
 for j in range(0, J_max):
  grid[i].append([1])

for i in range(0, I_max):
  for j in range(0, J_max):
   grid[i][j].append(pygame.Rect(i*dx, j*dy, dx, dy))
   grid[i][j].append(pygame.Color("Gray"))

details = [
[[-2, 0], [-1, 0], [0, 0], [1, 0]],
[[-1, 1], [-1, 0], [0, 0], [1, 0]],
[[1, 1], [-1, 0], [0, 0], [1, 0]],
[[-1, 1], [0, 1], [0, 0], [-1, 0]],
[[1, 0], [1, 1], [0, 0], [-1, 0]],
[[0, 1], [-1, 0], [0, 0], [1, 0]],
[[-1, 1], [0, 1], [0, 0], [1, 0]],
]

det = [[],[],[],[],[],[],[]]
for i in range(0, len(details)):
  for j in range(0, 4):
    det[i].append(pygame.Rect(details[i][j][0]*dx + dx*(I_max//2), details[i][j][1]*dy, dx, dy))

    
detail = pygame.Rect(0, 0, dx, dy)
det_choice = copy.deepcopy(random.choice(det))
count = 0

game = True
rotate = False
while game:
    delta_x = 0
    delta_y = 1
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
          exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                delta_x = -1
            elif event.key == pygame.K_RIGHT:
                delta_x = 1
            elif event.key == pygame.K_UP:
                rotate = True
    key = pygame.key.get_pressed()

if key[pygame.K_DOWN]:
    count = 31 * fps

screen.fill(pygame.Color("Black"))

for i in range(0, I_max):
    for j in range(0, J_max):
        pygame.draw.rect(screen, grid[i][j][2], grid[i][j][1], grid[i][j][0])

for i in range(4):
    if ((det_choice[i].x + delta_x * dx < 0) or (det_choice[i].x + delta_x * dx >= screen_x)):
        delta_x = 0
    if ((det_choice[i].y + dy >= screen_y) or (grid[int(det_choice[i].x//dx)][int(det_choice[i].y//dy) + 1][0] == 0)):
        delta_y = 0
        for i in range(4):
            x = int(det_choice[i].x // dx)
            y = int(det_choice[i].y // dy)
            grid[x][y][0] = 0 
            grid[x][y][2] = pygame.Color("White")
            detail.x = 0
    detail.y = 0
    det_choice = copy.deepcopy(random.choice(det))

for i in range(4):
        det_choice[i].x += delta_x*dx
count += fps

if count > 30 * fps:
    for i in range(4):
        det_choice[i].y += delta_y*dy
        count = 0

    for i in range(4):
        detail.x = det_choice[i].x
        detail.y = det_choice[i].y
        pygame.draw.rect(screen, pygame.Color("White"), detail)

C = det_choice[2] 
if rotate == True:
    for i in range(4):
        x = det_choice[i].y - C.y
        y = det_choice[i].x - C.x

        det_choice[i].x = C.x - x
        det_choice[i].y = C.y + y
        rotate = False

        for j in range(J_max - 1, -1, -1): 
            count_cells = 0
        for i in range(0, I_max): 
            if grid[i][j][0] == 0:
                count_cells += 1
            elif grid[i][j][0] == 1:
                break

        if count_cells == (I_max - 1):
            for l in range(0, I_max):
                grid[l][0][0] = 1 
            for k in range(j, -1, -1):
                for l in range(0, I_max):
                    grid[l][k][0] = grid[l][k-1][0]
pygame.display.flip()
clock.tick(fps)