Many web developers do not understand the difference between applying style to the body element versus the html element. Most of the time these authors will apply style only to the body element; when that's not sufficient, they'll spam all sorts of styles on both html and body until the page happens to look correct.
The confusion is understandable. In the beginning, both were treated similarly, with (now-deprecated) attributes like bgcolor being applied to the body tag, affecting the whole page.
This article attempts to enlighten you, Web Developer, to fully grok how these two elements are used in modern web browsers.