---

import turtle

window = turtle.Screen()
window.bgcolor('navy')
window.setup(600, 600)
window.title("Мяч, отскакивающий от стенок")

ball = turtle.Turtle('circle')
ball.turtlesize(2)
ball.color('red')
ball.penup()
ball.speed('fastest')

ball_x, ball_y = 0, 0
dx, dy = 2, 3
border_x = 280
border_y = 280

while True:
    ball_x += dx
    ball_y += dy

    ball.goto(ball_x, ball_y)

    if ball_x <= -border_x or ball_x >= border_x:
        dx = -dx
    if ball_y <= -border_y or ball_y >= border_y:
        dy = -dy

    window.update()