Of course. Just define them in the HTML/XHTML file before the <body> tag.
For example:
Code:
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Chapter-5.html</title>
<link href="../Styles/template_5.css" rel="stylesheet" type="text/css" />
</head>
<body>
...