Develop a program in Python language with a graphic interface that allows encryption decrypt a string of information using the Cesar code as a variant. You must request offset value

def cesar_cipher(text, offset):
    cipher = ''
    for i in range(len(text)):
        char = text[i]
        if char.isalpha():
            char = chr((ord(char) + offset - 97) % 26 + 97)
            cipher += char
    return cipher