If you have a class written to the body, effectively the top of the styleable document bits, the cascade starts flowing from the top! Effectively meaning you can get your hooks into almost anything below it without adding markup to said anythings.
Check out the stylesheet; "body.second h1" in human terms is "any h1 inside the body that has a class 'second' applied".
If you view the source of first and second dot html, you'll see that the page markup is identical except for the class written to the body tag (and of course the headline that identifies the page).