CSS questions

Hi there,
I use the Genesis framework. In the Genesis theme there is a CSS part that sets the global margins.

.entry {
	margin-bottom: 40px;
	padding: 50px 60px;
}

I managed to change a lot of the CSS by learning trial and error. I managed to change lot of the CSS of bbPress, but I don’t now how to change specific global things only affecting the bbPress forum.

How can I change only the margings and the font type of the forum, without affecting the rest of the site (Genesis CSS).

Your help is highly appreciated