createCanvas(100, 100);

  background(220);

  // 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);

​

  for (let i = 0; i <= 9; i++) {

    let x = i * 10;

    let y = i * 10;

    let size = 100 - x;

    let size2 = 100 - y;

    rect(x, y, size, size2);

  }

}

​