Why does the HTML5 DOCTYPE mess with my padding?

Question

I have an html5 page with a navbar. Completely scratch coded. I just recently added a doctype to the item, and now I’m getting extra space under my navbar. If I remove the docty

Answer 1

It's because the DOCTYPE changes the rendering mode to Standards Compliance Mode. Specifically, this means you're using the W3C Box Model now which computes width/height for block elements differently than quirks mode.

Read more here, here, and here.