SOURCE

function setup() {
   createCanvas(800,800);
   background(random(150),random(150),random(150));
}
function draw() { 
      for(let y=50;y<=height;y+=100){  
          for(let x=50;x<=width;x+=100){  
              stroke(random(0,360),random(0,360),random(0,360));
              fill(random(0,360),random(0,360),random(0,360));  
              ellipse(x,y,100,100);
 
          }
      }
}

 

<script src='https://cdn.jsdelivr.net/npm/p5@1.1.9/lib/p5.min.js'></script>