By Jennifer Kyrnin, About.com Guide
height property can be frustrating to use, because, especially if you are setting heights as a percentage of the browser window, they don't always work.
For example, this page you are on currently has a height set to this main content
div of 100%, and it is filling up the entire space, unlike the related example page.
Return to the FAQ: How do you set the height of an element to 100%? to learn how to get your elements to fill up the full height of a browser window.