SOURCE

function setup(){
    createCanvas(500,500);
    background(20);
}
function draw(){
    for(let x=0; x< height; x+=50){
        for(let y=0; y<height; y+=50){
    
         rect(x,y,50,50);
    }
  }
     for(let x=5; x< height; x+=50){
        for(let y=5; y<height; y+=50){
            fill(random(200),random(160),220);
         rect(x,y,40,40);
         
        }
     }
    for(let x=10; x< height; x+=50){
        for(let y=10; y<height; y+=50){
             fill(160,200,230);
         rect(x,y,30,30);
   }
    }
    for(let x=15; x< height; x+=50){
        for(let y=15; y<height; y+=50){
            fill(220,150,200);
         rect(x,y,20,20);
  }
    }
    for(let x=20; x< height; x+=50){
        for(let y=20; y<height; y+=50){
            fill(random(200),140,180);
         rect(x,y,10,10);
  }
    }
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>