Stylin' ChatZilla
ChatZilla's view window can be styled with CSS. These styles can be part of a full Mozilla skin, or can be distributed separately. To avoid confusion with a full blown Mozilla skin, ChatZilla refers to these sub-skins as "Motifs." You do not need to actually install a motif to use it, although you may if you like.
ChatZilla comes with a "null" motif, which has no colors or text styles associated with it. This motif has only basic font sizes, alignment, and emoticon urls, and uses your default foreground, background, and link colors. The null motif is located in ChatZilla's content directory, which means that it can not be overridden by a browser skin. You can always choose "No motif" from the View menu to revert to this motif, regardless of which browser skin you are using. This also lets you @import url(chrome://chatzilla/content/output-base.css); in your own ChatZilla motif, and count on it not changing out from under you when the user switches Mozilla skins.
In addition to the null motif, ChatZilla allows the browser skin to define three motifs of it's own. These motifs are called "default", "dark", and "light". The CSS files that define these motifs are chrome://chatzilla/skin/output-default.css, chrome://chatzilla/skin/output-dark.css, and chrome://chatzilla/skin/output-light.css respectively. A browser skin that contains style data for ChatZilla should override these files. It is possible to omit one, or all, of these motifs by providing a one line file that imports the base stylesheet, and setting the appropriate menu items to display: none; in chatzilla.css.
Creating a ChatZilla motif is very simple if you understand a little CSS. The ChatZilla output window is nothing but a HTML table. Each table row and cell contain enough attributes to determine the type of message, who sent it, and where it is displayed. Distributing a ChatZilla motif is even easier. Once you've got your CSS file the way you want it, put it somewhere on the web and tell people about it. They can use it by simply dragging the link onto their ChatZilla window. It will become their default motif, the next time they start ChatZilla the file will be reread from your server. If you update the motif, your users will automatically see the changes when they restart. For technical details on ChatZilla motifs, see the comment at the top of chrome://chatzilla/skin/output-default.css. Checking out the three motifs that come with the default ChatZilla skin may provide some enlightenment as well. To see these motifs in action (without actually running ChatZilla), visit the sample output window page.
If your users would prefer to install the file on their machine, they can do so by saving the file anywhere on their machine and typing ``/css <path-to-motif>''. Currently, ChatZilla does not include these external motifs in the view menu, although if someone cares enough to file a bug about it, that could change.
Many motifs are available at the ChatZilla website; if you have any questions or submissions, please join #chatzilla on irc.mozilla.org.