KnowledgeBuilder 2.50 introduced a new way to customize the look and feel of the public section of your KnowledgeBuilder by using the Smarty Templating Engine.
Template sets can be found (and new template sets should be placed in) the "templates" directory.
KnowledgeBuilder comes with three templates: Default, Tiny, and Directory, which you can copy and modify or use to learn more about how to create templates. New template sets that you create should be placed in their own directories underneath the "templates" directory with their own unique names. You can then choose which template set to use in the "General Settings" Admin section of your installation.
You can also modify the look and feel of your KB admin area by editing the smarty template files in the admin/templates/ directory.
One important piece of information to keep in mind if you want to create your own templates is about the use of the {debug} Smarty tag. If you place this tag in any template file, it will show you the available variables for that template.