CSS pseudo-classes can be used to style XHTML content in different ways.

In the XHTML:

<p class="author">Alex Milowski</p>

In the CSS:

p.author {
   font-size: 20pt;
   font-weight: bold;
   color: red;
}

A period in an element name means you need to escape it:

dot\.dot.class {
}

Example: (xhtml) (css)