YUIなしでcssをminifyする ref: http://qiita.com/items/95cd753fa824e5d2890e

file0.rb

require "sass"

css = <<CSS
body {
  color: red;
  background-color: black;
}

img.dokuro {
  display: inline-block;
  -moz-animation: spin 2s infinite linear;
  -o-animation: spin 2s infinite linear;
  -webkit-animation: spin 2s infinite linear;
  animation: spin 2s infinite linear;
}

body:before, body:after {
  content: "Welcome to Underground";
}
CSS

puts css
puts
puts "--- ↓ ---"
puts
puts Sass::Engine.new(css, :syntax => :scss, :style => :compressed).render

file1.css

body {
  color: red;
  background-color: black;
}

img.dokuro {
  display: inline-block;
  -moz-animation: spin 2s infinite linear;
  -o-animation: spin 2s infinite linear;
  -webkit-animation: spin 2s infinite linear;
  animation: spin 2s infinite linear;
}

body:before, body:after {
  content: "Welcome to Underground";
}

--- ↓ ---

body{color:red;background-color:black}img.dokuro{display:inline-block;-moz-animation:spin 2s infinite linear;-o-animation:spin 2s infinite linear;-webkit-animation:spin 2s infinite linear;animation:spin 2s infinite linear}body:before,body:after{content:"Welcome to Underground"}