### Replace the original import line with this:
from guizero import App, Text, TextBox, PushButton, Box, Combo, CheckBox, Slider

app = App(title="texteditor")

# function for reading files
def open_file():
    with open(file_name.value, "r") as f:
        editor.value = f.read()

# function for writing files
def save_file():
    with open(file_name.value, "w") as f:
        f.write(editor.value)

def change_font():
    editor.font = font.value

def change_color():
    editor.text_color = color.value

def change_bg_color():
    editor.bg = bg_color.value

def change_text_size():
    editor.text_size = size.value
    # resize the widget because if the text is made bigger, this might affect the size of the TextBox so guizero needs to know how to maintain the intended layout
    editor.resize(1, 1)
    editor.resize("fill", "fill")

# create a box to house the controls, we want the box to span the entire width of the app
file_controls = Box(app, align="top", width="fill")

# create a TextBox for the file name
file_name = TextBox(file_controls, text="text_file.txt", width=50, align="left")

# create a save button which uses the save_file function
save_button = PushButton(file_controls, text="Save",  align="right", command=save_file)

# create an open button which uses the open_file function
open_button = PushButton(file_controls, text="Open",  align="right", command=open_file)

# create a TextBox which is not in the box and fills the rest of the GUI
editor = TextBox(app, multiline=True, height="fill", width="fill", scrollbar=True)
editor.text_color="Green"
editor.bg="Purple"
preferences_controls = Box(app, align="bottom", width="fill", border=True)
preference_labels = Box(app, align="bottom", width="fill", border=True)
font = Combo(preferences_controls, options=["courier", "times new roman", "verdana"], align="left", command=change_font)
color = Combo(preferences_controls, options=["Yellow", "Green", "Blue", "Orange", "Pink", "Purple", "Red", "Cyan", "Black", "White"], selected="Green", align="left", command=change_color)
bg_color = Combo(preferences_controls, options=["Yellow", "Green", "Blue", "Orange", "Pink", "Purple", "Red", "Cyan", "Black", "White"],  selected="Purple", align="left", command=change_bg_color)
size = Slider(preferences_controls,  align="left", command=change_text_size, start=10, end=18)
text_font = Text(preference_labels,text="Font             Text Color    Bg Color       FontSize", align="left")
app.display()