Almost all pages on an OpenACS site use ACS Templating, and so their appearance is driven by a layer of different files. Let's examine how this works:
A templated page uses an ADP/TCL pair. The first line in the ADP file is usually:
If it appears exactly like this, without any arguments, the template processer uses default-master for that subsite. For pages in /var/lib/aolserver/$OPENACS_SERVICE_NAME/www, this is /var/lib/aolserver/$OPENACS_SERVICE_NAME/www/default-master.adp and the associated .tcl file.
The default-master is itself a normal ADP page. It draws the subsite navigation elements and invokes site-master (/var/lib/aolserver/$OPENACS_SERVICE_NAME/www/site-master.adp and .tcl)
The site-master draws site-wide navigation elements and invokes blank-master (/var/lib/aolserver/$OPENACS_SERVICE_NAME/www/blank-master.adp and .tcl).
Blank-master does HTML housekeeping and provides a framework for special sitewide navigation "meta" elements such as Translator widgets and Admin widgets.
/packages/acs-subsite/www/resources/site-master.css contains styles for the following elements:
/packages/acs-subsite/www/resources/default-master.css defines styles for the following elements:
/packages/acs-templating/www/resources contains many other css stylesheets that are appropriately named. Each package may also often have its own stylesheet.
Selva simplifies the work of customizing the look and feel of your OpenACS/dotLRN website. You will find Selva's documentation on each installation of openacs, once the package is installed, you will find its documentation as follows: http://yoursite/doc/theme-selva.
Since Selva is based purely on css you can have a better accessibility on designing your site.