Moving the mouse changes the position and size of each box. 

def setup():
    size(640, 360)
    noStroke()
    rectMode(CENTER)


def draw():
    background(51)
    fill(255, 204)
    rect(mouseX, height / 2, mouseY / 2 + 10, mouseY / 2 + 10)
    inverseX = width - mouseX
    inverseY = height - mouseY
    rect(inverseX, height / 2, (inverseY / 2) + 10, (inverseY / 2) + 10)