input: Write a python function to check if all words in a list are contained in a given input string.
  assert contains_words('This is a test', ['test', 'this', 'is']) == True
  assert contains_words('This is a test', ['test', 'this', 'is', 'example']) == False
  assert contains_words('Hello world', ['hello', 'world']) == True
  assert contains_words('Python programming', ['python', 'java']) == False
output: def contains_words(input_string, words):
      input_string = input_string.lower()
      return all(word.lower() in input_string for word in words)