Q:

Node.js Express - How do I compile Stylus .styl files into CSS

I'm trying to build an application starting from Balloons (http://balloons.io), which uses Backbone.js and express to setup the UI.  I've never used these frameworks, and I'm having a hard time actually making changes. 
As I understand it, .styl files are compiled into CSS files.  How do I do this compilation? 

A:

For production systems you'd use a stylus executable to convert .styl to .css before deployment.  It's as easy as doing:
stylus css --out stylesheet_dir

in the folder where your .styl files reside. 
For development you can use stylus middleware to convert files on the fly.