createCanvas(100, 100);

  background(220);

  for (let c=0; c<=90; c+=10){

    rect (c, c, 100-c, 100-c)

  }

  // (0) 100-c= 100

  //(10) 100-c= 90

  // (20)100-c= 80

  // rect(0, 0, 100, 100);

  // rect(10, 10, 90, 90);

  // rect(20, 20, 80, 80);

  // rect(30, 30, 70, 70);

  // rect(40, 40, 60, 60);

  // rect(50, 50, 50, 50);

  // rect(60, 60, 40, 40);

  // rect(70, 70, 30, 30);

  // rect(80, 80, 20, 20);

  // rect(90, 90, 10, 10);

}

​

​