Code Not Working

import tkinter as tk


class Pymodoro:
    def __init__(self, master):
        self.master = master
        self.main_frame = tk.Frame(
            self.master,
            bg='white'
        )
        self.main_frame.pack(
            fill=tk.BOTH,
            expand=True
        )
        self.build_grid()

    def build_grid(self):
        self.main_frame.columnconfigure(0, weight=1)
        self.main_frame.rowconfigure(0, weight=1)
        self.main_frame.rowconfigure(2, weight=0)

    def build_banner(self):
        banner = tk.Label(
            self.main_frame,
            bg='red',
            text='Pymodoro',
            fg='white',
            font=('Helvetica', 24)
        )
        self.banner.grid(
            row=0,
            column=0,
            sticky='we',
            padx=10,
            pady=10
        )


if __name__ == '__main__':
    root = tk.Tk()
    Pymodoro(root)
    root.mainloop()