Python GUI guizero: Box layout: Box in Box

# guizero - Hero name generator .. Box in Box
# Design principles .. repetition, proximity, ...
from guizero import App, Text, ButtonGroup, Combo, PushButton, TextBox, Box
app = App(title="Hero-o-matic", width=600, height=690)
app.bg = "#CCCC00"

# Function definitions for your events go here.
def make_hero_name():
    adjective = bgp_adjective.value
    colour = txt_cText.value
    animal = cmb_animal.value
    hero = adjective + " " + colour + " " + animal
    lbl_output.value = "You are... The " + hero + "."

# STYLING: define some Colour constants
cSubHead   = "#FFFFFF"
cSubHeadBg = "#000000"
txtSizeSubHead = 14
widthSubHead   = 28
#------------
# GUI widgets
h1 = Text(app, text="Hero-o-matic name builder", size=26, font="Times New Roman")

boxForm = Box(app, width=400, height=600)
boxForm.bg = "cyan"
# now add widgets inside 'form' Box

boxAdj = Box(boxForm, width="fill", height=190)
boxAdj.bg = "#74CC9F"
boxAdj.text_color = "#123456"

message1 = Text(boxAdj, text="Please choose an adjective ..", width=widthSubHead )
message1.text_color = cSubHead
message1.bg = cSubHeadBg
message1.text_size = txtSizeSubHead

bgp_adjective = ButtonGroup(boxAdj, options=["Amazing", "Bonny", "Charming", "Delightful", "Vundebar"], selected="Amazing")
#-------------
boxColor = Box(boxForm, width="fill", height=90)
boxColor.bg = "#54AA7F"
boxColor.text_color = "white"

message2 = Text(boxColor, text="Please enter a colour name ..", width=widthSubHead )
message2.text_color = cSubHead
message2.bg = cSubHeadBg
message2.text_size = txtSizeSubHead

vertSpace01 = Text(boxColor, text=" ", width="fill", size=12 )
txt_cText = TextBox(boxColor)
txt_cText.bg="white"
txt_cText.text_color = "black"
txt_cText.text_size = 18
#-----------
boxAni = Box(boxForm, width="fill", height=90)

message3 = Text(boxAni, text="Please pick an animal ..", width=widthSubHead )
message3.text_color = cSubHead
message3.bg = cSubHeadBg
message3.text_size = txtSizeSubHead
vertSpace02 = Text(boxAni, text=" ", width="fill", size=12 )

cmb_animal = Combo(boxAni, options=["Aardvark", "Badger", "Cat", "Dog", "Dolphin", "Velociraptor"], selected="Aardvark", width=20)
cmb_animal.text_color = "#FFFFFF"
cmb_animal.bg = "#FF0000"

btn_make_name = PushButton(boxForm, text='Make me a hero', command= make_hero_name )
btn_make_name.bg = "#EE66EE"
btn_make_name.text_color = "white"
#-----------
boxOut = Box(boxForm, width="fill", height=90)

lbl_output = Text(boxOut, text="A hero name will appear here", align="bottom")

# Set up event triggers here

# Show the GUI on the screen, start listening to events.
txt_cText.focus()
app.display()