How to create a custom 'fluid' layout in Display Suite 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.
Just select the custom layout in the Manage Display page:



And add the required CSS in your theme. See the examples included in Display Suite: