This is the body font, it should be black Arial 12px heigh.

This is a paragraph, it should be black Arail 18px heigh.

This is a paragraph, it should be gree Arail 18px heigh.

This is a paragraph, it should be black Arail 18px heigh. But this part should be green.

This is a level 2 heading, it should be green Arail. The same class could be applied to a list, a block quote or whatever