SOURCE

function setup(){
    createCanvas(500,500);
    background(255);
}
function draw(){
    for(let x=0; x<500; x+=40){
        for(let y=0; y<500; y+=40){
        stroke(random(360),100,100)
        fill(random(360),100,100);
        rect(x,y,random(50));
    }
  }
}

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