def setup
  createCanvas(100, 100)
  background(0)
  button = createButton('Action')
  button.position(0, 0)
  button.mousePressed do
    @g = rand(255)
    @d += 10
    @d = 10 if @d > 100
  end
  @g = 220
  @d = 10
end

def draw
  background(@g)
  ellipse(width / 2, height / 2, @d, @d)
end