Creating custom CSS for a book
In Drupal 7, you can add a CSS class to the &lt;body&gt; tag for your book. For nodes, you have the class added by default. For example page-node-2056, for the /node/2056 path.

For Book nodes, you might add the book ID inside your template.php theme file, in the theme_preprocess_html function:

function MYTHEME_preprocess_html(&amp;$vars) {
  // If on an individual node page, add the book ID to body classes.
  if ($node = menu_get_object()) {
    if (isset($node-&gt;book['bid'])) {
      $vars['classes_array'][] = drupal_html_class('book-id-' . $node-&gt;book['bid']);
    }
  }
}


You can then take the ID for each book and add all the style definitions in a single CSS file. Something like the following:

.book-id-xxx {
  /* Style for book xxx. */
}
.book-id-yyy {
  /* Syle for book yyy. */
}
... and so on


Would it make sense for what you need?