Cascading riddle

Well, do you think, you understand CSS and browsers? So you can try this riddle.

On the example page you will see a few colored streaks and your work is discover, where are the streaks defined without taking a look at the external CSS. The important thing is, that I don't use CSS property border. If I use it, there will be more and more streaks. In the site is no images, there are only HTML and Cascading Styles. And in the end don't look at the page in MSIE because this browser is susceptible to show pages... Unusual.

The page: Cascading riddle