import pygame
pygame.init()

screen = pygame.display.set_mode([500, 500])
RED = (255, 0, 0)
a = 10
b = 10
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
            
        if event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
                a+= 10
                b+= 10
            if event.button == 3 and a >=10:
                a-= 10
                b-= 10
    screen.fill((255, 255, 255))

    pygame.draw.rect(screen,RED, (250-a/2,250-b/2, a, b))

    pygame.display.flip()

pygame.quit()