SOURCE

function setup(){
    createCanvas(500,500);
    background(200);
    noStroke();
    rectMode(CENTER);
    colorMode(HSB,360,100,100)
}

function draw(){
    for(let x=25; x<500; x+=50){
        for(let y=25;y<500;y+=50){
            fill(random(255),100,100);
            rect(x,y,random(50),random(50));
            ellipse(x,y,random(30),random(30));
        }
    }
}

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