Python GUI guizero: FULL SCREEN resize

# Under 'PushButton control', this demo resizes (and colours) the h1 heading
# and switches in and out of FULL SCREEN mode
from guizero import App, Text, Box, PushButton

app = App(title="REsize")
app.bg ="cyan"

fullSize = True #

def changeSize():
    global fullSize
    fullSize = not(fullSize) # toggle

    if (fullSize):
        sizingButton.text = "EXIT Full Screen mode"
        h1.text_size = 30
        h1.width = 40
        h1.text_color = "red"
        app.set_full_screen()
    else:
        sizingButton.text = "ENTER Full Screen mode"
        h1.text_size = 20
        h1.width = 26
        h1.text_color = "black"
        app.exit_full_screen()


vertSpace01 = Text(app, text=" ", width="fill", size=12 )
h1 = Text(app, text="Header text - resizes", align="top")
h1.bg = "white"

box1 = Box(app)
box1.bg = "#FE3456"

a_text = Text(box1, text="Same size ..?", align="bottom")
sizingButton = PushButton(app, text='GO !', command= changeSize )
sizingButton.bg = "#EE66EE"
sizingButton.text_color = "white"
sizingButton.text_size = 20

changeSize() # set initial config
app.display()