import turtle
wn = turtle.Screen()
wn.bgcolor("lightgreen")
tess = turtle.Turtle()

def draw_square(t,size):
    for i in range(4):
        tess.forward(size)
        tess.left(90)

size = 20
for j in range(3):
   tess.pensize(3)
   draw_square(tess,size)
   size = size + 20
   tess.penup()
   tess.goto(-20, -20)
   tess.pendown()

wn.mainloop()