尝试验证表单时，PHP不会显示HTML

This is my first real attempt at coming to StackExchange and I wanted my question to be as relevant as possible. Basically, I am following along in the O'Reilly book to Learn PHP, MySQL, Javascript, etc. and I'm a bit stuck on Chapter 16's authentication protocol. Basically the author wants us to just put the CSS and JS in the echo <<<_END statements, I'm trying to put it so they can still be kept separate in their external file. This is my first real attempt at coming to Stac