main.py

import tkinter as tk
# from tkinter import ttk
import ttkbootstrap as ttk


def main():
    def convert():
        mile_input = entry_int.get()
        km_output = mile_input * 1.61
        print(entry_int.get())
        output_string.set(km_output)

    # window
    window = ttk.Window(themename="darkly")
    window.title("Demo")
    window.geometry("300x150")

    # title
    title_label = ttk.Label(master=window, text="Miles to kilometers", font="Arial 20")
    title_label.pack()

    # input_field
    input_frame = ttk.Frame(master=window)
    entry_int = tk.IntVar()
    entry = ttk.Entry(master=input_frame, textvariable=entry_int)
    button = ttk.Button(master=input_frame, text="Convert", command=convert)
    entry.pack(side="left", padx=10)
    button.pack(side="left")
    input_frame.pack(pady=10)

    # output
    output_string = tk.StringVar()
    output_label = ttk.Label(
        master=window,
        text="Output",
        font="Calibri 30",
        textvariable=output_string)
    output_label.pack()

    # run
    window.mainloop()


if __name__ == '__main__':
    main()