input: from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt_decrypt_strings(operation: str, text: str) -> str:
      """
      Encrypt or decrypt the given string using AES encryption in ECB mode.
      The function accepts two parameters: 'operation' which should be either 'encrypt' or 'decrypt',
      and 'text' which is the string to be encrypted or decrypted.
      >>> encrypt_decrypt_strings('encrypt', 'Hello World')
      b'\\x8b\\xafG\\xe4\\x1e\\x87\\xffmqq\\xf9\\x9e?W\\xa0\\xc4E'
      >>> encrypt_decrypt_strings('decrypt', b'\\x8b\\xafG\\xe4\\x1e\\x87\\xffmqq\\xf9\\x9e?W\\xa0\\xc4E')
      'Hello World'
      """
      if operation not in ['encrypt', 'decrypt']:
          raise ValueError("Operation must be either 'encrypt' or 'decrypt'.")
      
      cipher = AES.new(key, AES.MODE_ECB)
      
      if operation == 'encrypt':
          return cipher.encrypt(text.encode())
      elif operation == 'decrypt':
          return cipher.decrypt(text).decode()
output:     if len(text) % 16 != 0:
          raise ValueError("The input text length must be a multiple of 16 bytes for decryption.")