//createCanvas(800, 400);

//}

​

//function draw() {

  //background(220);

    //top

  //line (200,100,600,100)

    //bottom

  //line(200,300,600,300)

    //left

  //line(200,100,200,300)

    //right

  //line(600,100,600,300)

//}

​

let a, b, c, d

​

function setup() {

  createCanvas(1000, 400);

  a = 0.25 * width;

  b = 0.25 * height;

  c = 0.75 * width;

  d = 0.75 * height;

}

​

function draw() {

  background(220);

  line(a,b,c,b)

  line(a,d,c,d)

  line(a,b,a,d)

  line(c,b,c,d)

}