SOURCE

function setup() { 
    createCanvas(800,800);
    background(random(405),random(405),random(405));  
    noFill();
    colorMode(HSB,360,25,100); 
 }
 
 function draw() {
       for(let y=0;y<=height;y+=100){  
           for(let x=0;x<=width;x+=100){   
               stroke(random(405),random(405),random(405));
               fill(random(405),random(405),random(405));  
               rect(x,y,75,75);
               rect(x+8,y+8,84,84);
               rect(x+16,y+16,68,68);   
               rect(x+24,y+24,52,52); 
               rect(x+32,y+32,36,36);
           }
       }
 }

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