Aaaand YouTube forced a layout update that makes everything stretched to the screen. @YouTube @TeamYouTube Really? Stuff being centred was better, even if it had unused white space on the sides, now it's awful!
Your HTML code is broken. Divs with the ID "content" are missing the class "content-alignment". This code alone fixes it: var content = document.getElementById ("content"); content.classList.add ("content-alignment");