It is recommended to add class="youtube" like following:

<iframe
  class="youtube"
  src="https://www.youtube.com/embed/33pe6pnw9C8?controls=0"
  title="YouTube video player"
  frameborder="0"
  allow="accelerometer;fautoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
  allowfullscreen></iframe>