input: def login_automation(website: str, username_value: str, password_value: str) -> str:
      """ Automate the login process on a given website using Selenium.
      After a successful login, it prints 'Login successful!' and closes the browser.
      >>> login_automation('http://www.example.com', 'username', 'password')
      'Login successful!'
      """
output:     from selenium import webdriver
      from selenium.webdriver.common.by import By
      from selenium.webdriver.common.keys import Keys
      import time
  
      driver = webdriver.Chrome()
      driver.get(website)
  
      username = driver.find_element(By.NAME, 'username')
      password = driver.find_element(By.NAME, 'password')
  
      username.send_keys(username_value)
      password.send_keys(password_value)
      password.send_keys(Keys.RETURN)
  
      time.sleep(2)
  
      success_message = 'Login successful!'
      print(success_message)
  
      driver.quit()
      return success_message