let rotation_speed = 0.01;

​

function setup() {

  createCanvas(400, 400);

​

  // set the origin point for the rect() to its center

  rectMode(CENTER);

}

​

function draw() {  

  background(100, 0, 200);

  strokeWeight(10);

  // move everything to the center of the canvas

  translate(width/2, height/2);

  // draw a rect() before rotating

  stroke(0, 255, 255);

  fill(255, 255, 0);

  rect(0, 0, 250, 250);

  // rotate the second rect();

  rotate(90);

  stroke(255, 0, 255);

  fill(255, 0, 0);

  rect(0, 0, 100, 100);

}