Using CSS preprocessors effectively

by Jonas Wagner

  • Known for doing crazy and creative stuff
  • Porting Physic engines to JavaScript via Python
  • Works as Software Engineer at
  • 3.1 million unique clients

Don’t make a mess

  • Most programming languages encourage good code pattern
  • CSS is not one of those languages

Issues with CSS

  • No Variables
  • No hierarchy
  • Prefixes
  • Sprites
  • Lack of abstraction

Solution: CSS Preprocessors

Choosing a Preprocessor


  • Official implementation is in Ruby
  • Two dialects scss and sass
  • Sassy CSS
  • Syntactically Awesome Stylesheets
  • PySCSS is an implementaton of SCSS in Python
  • Compass is


  • Originally written in Ruby
  • Now implemented using JavaScript in Node.js
  • Can be compiled on the client and using Node.js
  • Twitter bootstrap uses LESS

Which one?

  • Features virtually equivalent

  • Both are a superset of CSS

  • He recommends SCSS

    • More explicit syntax
    • Compass offers lots of goodies
    • Decent Python implementation

Common Features

  • Variables
  • math and functions
  • nesting
  • avoiding CSS hacks
  • More elegant comment system
  • Mixins
  • Prefixes

Doing it with Django

pip install webassets cssmin



from django_assets import Bundle, register
js = Bundle('common/jquery.js', 'site/base.js', 'site/widgets.js',
            filters='jsmin', output='gen/packed.js')
register('js_all', js)
{% load assets %}
{% assets "js_all" %}
    <script type="text/javascript" src="{{ ASSET_URL }}"></script>
{% endassets %}


  • Good editor support for Preprocessors
  • Graphical tools like LiveReload and
  • FireSASS


  • Increased complexity
  • Might not work with IE
  • Makes debugging harder
  • Potential for bloat


  • Preprocessors solve common problems
  • Allow us to focus on writing clear and meaningful CSS
  • Try it on at least one project
  • Plain old CSS feels very silly