Using multiple CSS classes on an element can be powerful, and a time-saver. Here’s a simple example, let’s say you want to add a class called red to make certain text elements stand out. Try this:
<span class="boldtext red">for sale</a>
In the sample above, the text “for sale” will have the class boldtext and red applied to it. Multiple classes can be really helpful if you start working on a site you didn’t write, and don’t have the time to map out the previous web dude’s CSS fully, or even if you are just in a hurry, or your stylesheet has grown so big over time you want to place it safe.