I'm trying omega and adaptivetheme to use responsive webdesign. On omega that uses 960grid, I can add a "grid-X" class to an html element to display it in the grid, with the right width etc. Is there a way to do the same thing with adaptivetheme?
AT does not use Grid classes embedded in markup (it does not use grid classes at all).
If you are asking this I assume you do not really understand how this theme works - you use the layout system (in theme settings, for the main container/page and panels layouts) and write content/element specific CSS yourself, aka use a semantic grid approach.
Grid classes in markup are a huge limitation - what seems so easy now, turns quickly into a massive roadblock later on.
answer by author of adaptivetheme http://drupal.org/node/1861948