DRY stylesheets with nested selectors and variables. No new syntax to learn :-)

CssDryer – Eliminate Repetition In Your Stylesheets


Cascading style sheets (CSS) are wonderful but repetitive. Repetition is bad, so CssDryer lets you write CSS without repeating yourself. And you don’t need to learn any new syntax.

There are two sources of repetition in CSS:

  • nested selectors
  • lack of variables

Nested selectors lead to CSS like this:

div           { font-family: Verdana; }
div#content   { background-color: green; }
div#content p { color: red; }

Note the triple repetition of div and the double repetition of #content.

The lack of variables leads to CSS like this:

.sidebar { border: 1px solid #fefefe; }
.content { color: #fefefe; }

Note the repeated colour #fefefe.

CssDryer eliminates both of these. The examples above become:

<% dark_grey = '#fefefe' %>

div {
  font-family: Verdana;
  #content {
    background-color: green;
    p { color: red; }

.sidebar { border: 1 px solid <%= dark_grey %>; }
.content { color: <%= dark_grey %>; }

Note, though, that @media blocks are preserved. For example:

@media screen, projection {
  div {font-size:100%;}

is left unchanged.

The original whitespace is preserved as much as possible.

Which Selectors Are Supported?

CssDryer handles all CSS 2.1 selectors: nested descendant, child, adjacent, class, pseudo-class, attribute and id selectors.

Multiple comma separated selectors are also supported.


Comments on nested selectors do not get ‘flattened’ or de-nested with their selector. For example comment B will be left inside the html selector below:


/* Comment A */
html {
  /* Comment B */
  p {
    color: blue;


/* Comment A */
html {
  /* Comment B */
html p {
  color: blue;

This is suboptimal but I hope not too inconvenient.

Please also note that commas in comments will sometimes be replaced with a space. This is due to a shameful hack in the code that handles comma-separated selectors.


You may use partial nested stylesheets as you would with normal templates. For example, assuming your controller(s) set the @user variable and a User has a background colour (red):


body {
  color: blue;
  <%= render :partial => 'content', :locals => {:background => @user.background} %>


div#content {
  background: <%= background %>;
  margin: 10px;

And all this would render to site.css:

body {
  color: blue;
body div#content {
  background: red;
  margin: 10px;

Remember the helper

Browser hacks are an ugly necessity in any non-trivial stylesheet. They clutter up your stylesheet without actually adding anything. They make you sad.

So encapsulate them in the StylesheetsHelper instead. Separate your lovely CSS from the decidely unlovely hacks. For example:


<% ie7 do %>
  #sidebar {
    padding: 4px;
<% end %>

This renders to site.css:

*+html #sidebar {
  padding: 4px;

In this example the hacky selector, *+html, isn’t too bad. However some hacks are pretty long-winded, and soon you’ll thank yourself for moving them out of your nested stylesheet.

You don’t have to limit yourself to browser hacks. Consider self-clearing: to make an element clear itself requires 13 lines of CSS, in 3 selector blocks, by my count. To make a second element clear itself, you need to add the element’s selector to each of those three blocks. It’s fiddly. And your stylesheet gets harder and harder to understand.

We can do better:


<%= self_clear 'div.foo', 'div.bar', 'baz' %>

Self-clear as many elements as you like in one easy line.


Pre-requisite: Rails 2.2.

First, install in the usual Rails way. From your application’s directory:

$ script/plugin install git://github.com/airblade/css_dryer.git

Second, generate the stylesheets controller and helper, and a test nested stylesheet:

$ script/generate css_dryer

Third, add a named route to your config/routes.rb:

map.stylesheets 'stylesheets/:action.:format', :controller => 'stylesheets'

Verify that everything is working by visiting this URL:

You should see this output:

body {
  color: blue;
body p {
  color: red;


You put your stylesheets, DRY or otherwise, in app/views/stylesheets/. Once rendered they will be cached in public/stylesheets/.

DRY stylesheet files should have a ncss extension – think ‘n’ for nested. For example, site.css.ncss.

Get them in your views with a css extension like this:

<link href='/stylesheets/site.css' rel='Stylesheet' type='text/css'>

or with Rails’ stylesheet_link_tag helper:

<%= stylesheet_link_tag 'site' %>

To Do

  • Make CssDryer work with Rails’ asset packaging: incorporate Dan Walters’ code on GitHub.
  • Replace regexp-based nested-stylesheet parser with a Treetop parser.
  • Package as a gem as well as a plugin.
  • Configuration, e.g. #implicit_nested_divs = true
  • Merb compatibility.
  • Split out a separate EXAMPLES document.
  • Rake task to generate and write .css files from .ncss ones.
  • Port to Java/JSP/Servlet to bring a little ray of sunshine to J2EE webapp programming.


  • RCSS: ERB, server-side constants, server-side classes and command line execution. No nesting as such, though server-side classes offer a form of inheritance.

  • DCSS (written up here): server-side constants, different syntax. Descendant selectors only.

  • Styleaby creates CSS with Ruby syntax. “An experimental, unauthorized mashup of Scott Barron’s stillborn Builder::CSS templates and Why The Lucky Stiff’s Markaby templates.”

  • Dirt Simple .rcss Templates by Josh Susser. No nesting, just variables.


The idea came from John Nunemaker on Rails Tips. John beta-tested the code, provided a test case for @media blocks and suggested the controller’s body. Thanks John!

The caching code is based on Topfunky’s.

Changing the controller’s name to stylesheets, thus allowing one to use Rails’ stylesheet_link_tag helper, occurred to me while reading Josh Susser’s Dirt Simple .rcss Templates. Once I noticed it, I realised everybody was using a StylesheetsController. Doh!


Andrew Stewart, AirBlade Software Ltd.


CssDryer is available under the MIT licence. See MIT-LICENCE for the details.

Copyright © 2006-2008 Andrew Stewart

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