Getting Darker
This is one detail you will only notice if you decide to have a Harry Potter marathon. The movies start off innocent and happy enough – with a bunch of young wizards who go to school, learn magic, play Quidditch, and sometimes get into trouble.
Of course, as the movies progress the stories get darker – there are scary Dementors and other creatures, nasty fights between friends, battles and wars, emotional deaths, and more deaths. The filmmakers realized how it all plays out so they decided to mimic the darkness with a progressively grimmer “Warner Bros” logo in each successive movie.