closed_sqaure

function setup() {
  var a = 150;
createCanvas(500,500);
background(255);
fill(0);
rect(350,0, a,a);
rect(350,350,a,a);
rect(0,0,a,a);
rect(0,350,a,a);
}

function draw() {
  fill(255,255,255);
  rectMode(CENTER);
  noStroke();
  rect(width/2,height/2,300,300);
}