Trouble setting up a custom theme environment for AsciiDoctor

I realize that this may be more of a SASS or Compass question, but give it a try here in anticipation that others have encountered the same:

I've grabbed the asciidoctor-stylesheet-factory on Github and have Ruby with all necessary gems installed. Building the included stylesheets with "compass compile" works fine. Then I try to build my own customized theme, following the instructions under "Create a theme" in the README.adoc file in the repository.

I am building a theme named "svv" and svv.scss contains

 @import "settings/svv";
 @import "components/asciidoc";
 @import "components/awesome-icons";

as suggested by the documentation. I've created an empty _svv.scss under sass/settings. Compiling with compass again gives this error:

   error sass/svv.scss (Line 4 of _grid.scss: Undefined variable: "$include-html-classes".)
   create stylesheets/svv.css

"grid" is a foundation component, and foundation is installed. So I define $include-html-classes in _svv.scss and do a new compile:

    error sass/svv.scss (Line 52 of _grid.scss: Undefined variable: "$default-float".)
overwrite stylesheets/svv.css

I can do the same again and move one step further in the compilation, but the story repeats - it is clear that I am missing some definitions in my setup, probably some Foundation related things.

I would expect the example in the documentation to work out the box, but it is probably easy to fix. Any idea which imports are missing in my svv.css to have decent defaults for all uses SASS variables?? Any additional modules in config.rb I need to require?

Thanks for any help on this,

-steinar