How can I make the tkinter window fixed?

This is my current code, and I am struggling to understand where I need to put additional code to make sure that my tkinter window is fixed. Code taken from: https://pythonprogramming.net/change-show-new-frame-tkinter/

import tkinter as tk


LARGE_FONT= ("Verdana", 12)


class SeaofBTCapp(tk.Tk):

    def __init__(self, *args, **kwargs):
        
        tk.Tk.__init__(self, *args, **kwargs)
        container = tk.Frame(self)

        container.pack(side="top", fill="both", expand = False)

        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}

        for F in (StartPage, PageOne, PageTwo):

            frame = F(container, self)

            self.frames[F] = frame

            frame.grid(row=0, column=0, sticky="nsew")
            

        self.show_frame(StartPage)

    def show_frame(self, cont):

        frame = self.frames[cont]
        frame.tkraise()

        
class StartPage(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self,parent)

        label = tk.Label(self, text="NC's Ice-Cream Shop", font=LARGE_FONT)
        label.pack(pady=10,padx=10)

        button = tk.Button(self, text=">>",
                            command=lambda: controller.show_frame(PageOne))
        button.pack()

        #button2 = tk.Button(self, text="Visit Page 2",
            #                command=lambda: controller.show_frame(PageTwo))
        #button2.pack()


class PageOne(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text="Order Details", font=LARGE_FONT)
        label.pack(pady=10,padx=10)

        button1 = tk.Button(self, text="<<",
                            command=lambda: controller.show_frame(StartPage))
        button1.pack()

        button2 = tk.Button(self, text=">>",
                            command=lambda: controller.show_frame(PageTwo))
        button2.pack()


class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text="Receipt", font=LARGE_FONT)
        label.pack(pady=10,padx=10)

        button1 = tk.Button(self, text="<<",
                            command=lambda: controller.show_frame(PageOne))
        button1.pack()

        button2 = tk.Button(self, text="New",
                            command=lambda: controller.show_frame(StartPage))
        button2.pack()
        



app = SeaofBTCapp()
app.mainloop()

Answer

As mentioned in the comments, you simply need to set your root window resizable method to false. In your case it is the SeaofBTCapp class.

For Example:

import tkinter as tk

LARGE_FONT= ("Verdana", 12)

class SeaofBTCapp(tk.Tk):

    def __init__(self, *args, **kwargs):

        tk.Tk.__init__(self, *args, **kwargs)
        self.resizable(False,False)   # <------------------- added this

        container = tk.Frame(self)
        container.pack(side="top", fill="both", expand = False)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in (StartPage, PageOne, PageTwo):
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame(StartPage)

    def show_frame(self, cont):
        frame = self.frames[cont]
        frame.tkraise()


class StartPage(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self,parent)
        label = tk.Label(self, text="NC's Ice-Cream Shop", font=LARGE_FONT)
        label.pack(pady=10,padx=10)
        button = tk.Button(self, text=">>",
                            command=lambda: controller.show_frame(PageOne))
        button.pack()

        #button2 = tk.Button(self, text="Visit Page 2",
            #                command=lambda: controller.show_frame(PageTwo))
        #button2.pack()

class PageOne(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text="Order Details", font=LARGE_FONT)
        label.pack(pady=10,padx=10)
        button1 = tk.Button(self, text="<<",
                            command=lambda: controller.show_frame(StartPage))
        button1.pack()
        button2 = tk.Button(self, text=">>",
                            command=lambda: controller.show_frame(PageTwo))
        button2.pack()


class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text="Receipt", font=LARGE_FONT)
        label.pack(pady=10,padx=10)
        button1 = tk.Button(self, text="<<",
                            command=lambda: controller.show_frame(PageOne))
        button1.pack()

        button2 = tk.Button(self, text="New",
                            command=lambda: controller.show_frame(StartPage))
        button2.pack()

app = SeaofBTCapp()
app.mainloop()