HTML5 vs HTML4 - h1 tag rendered with extra space - how to remove?

Question

I took a page whose DTD was HTML4 Transitional and changed the doctype to and extra space appeared between the h1 and div beneath it. I

Answer 1

Your bug deals with default line height.

The HTML4 transitional is ignoring the contents of your H1 wrt line height, yielding a 25px tall element. The HTML5 is respecting the line-height of the H1 tag, which equates to 29px.