title: Twitter bootstrap has Invalid CSS according to Rails 3.1 asset pipeline during precompilation?
body: <p>I created a brand new Rails 3.1 app. I added the twitter bootstrap CSS file in app/assets/stylesheets/bootstrap.min.css. Here is the relevant code</p>
  
  <p>app/assets/stylesheets/application.css (includes the tree, so bootstrap is included)</p>
  
  <pre><code>/*
   * This is a manifest file that'll automatically include all the stylesheets available in this directory
   * and any sub-directories. You're free to add application-wide styles to this file and they'll appear at
   * the top of the compiled file, but it's generally better to create a new file per style scope.
   *= require_self
   *= require_tree . 
  */
  </code></pre>
  
  <p>Gemfile (includes execjs and therubyracer for compile/compress)</p>
  
  <pre><code>group :development, :qa do
    gem 'execjs'
    gem 'therubyracer'
  end
  # Gems used only for assets and not required
  # in production environments by default.
  group :assets do
    gem 'sass-rails',   '~&gt; 3.1.0'
    gem 'coffee-rails', '~&gt; 3.1.0'
    gem 'uglifier', '&gt;= 1.0.3'
  end
  </code></pre>
  
  <p>Then I run the rake task to precompile assets</p>
  
  <pre><code>rake assets:precompile
  </code></pre>
  
  <p>this fails with the following error</p>
  
  <pre><code>Invalid CSS after ".inputs-list li+": expected number or function, was "li"
  </code></pre>
  
  <p>that CSS is in the bootstrap file (".inputs-list li+li" is the selector).</p>
  
  <p>However, if I run </p>
  
  <pre><code>rake assets:precompile RAILS_ENV=development
  </code></pre>
  
  <p>now it works fine. Turns out that if I change config/environments/production.rb to not compress files:</p>
  
  <pre><code>config.assets.compress = false
  </code></pre>
  
  <p>then the original command works too (without specifying development environment). </p>
  
  <p>So, how do I track down the error? I can live with just turning off compression for now, but obviously something is wrong. Is it Rails? Sprockets? The Ruby Racer? Uglifier?</p>