Add a standard button box.

        Override if you do not want the standard buttons

def buttons(self, master):
        '''Add a standard button box.

        Override if you do not want the standard buttons
        '''

        box = tk.Frame(master)

        ttk.Button(
            box,
            text="Next",
            width=10,
            command=self.next_day
        ).pack(side=tk.LEFT, padx=5, pady=5)
        ttk.Button(
            box,
            text="OK",
            width=10,
            command=self.ok,
            default=tk.ACTIVE
        ).pack(side=tk.LEFT, padx=5, pady=5)
        ttk.Button(
            box,
            text="Cancel",
            width=10,
            command=self.cancel
        ).pack(side=tk.LEFT, padx=5, pady=5)

        self.bind("n", self.next_day)
        self.bind("<Return>", self.ok)
        self.bind("<Escape>", self.cancel)

        box.pack()