I created a Display suite custom layout following this tutorial: https://drupal.org/node/1098068
It works fine, but I need this custom layout to be Fluid.
In Display Suite, the "fluid" refers to the templates ability to expand the column width if one (or more) columns are empty.
How can I do this? I guess I need to add some php code which will add some extras css classes. But I don't know how and where to add this code.