createCanvas(windowWidth, windowHeight);

  colorMode(HSB, 360, 100, 100, 100);

}

​

function draw() {

  let bgCol = map(mouseX, 0, width, 0, 360);

  background(bgCol, 100, 100);

  translate(width / 2, height / 2);

  let a = atan2(mouseY - height / 2, mouseX - width / 2);

  rotate(a);

  rectMode(CENTER);

  rect(0, 0, 200, 50);

}