The zen and zen-based themes are very customizable, so to make these themes work, you have to use the sample config file.
Three variants of Zen are available:
zen, based on Mako templates
zen-jinja, based on Jinja2 templates
zen-forkawesome, using ForkAwesome icons instead of FontAwesome, based on Mako Templates
WARNING: The themes use Less for their styles, but you don't need a Less compiler installed to use it.