Welcome to Sass. The world premier CSS pre-processor. All others fail in comparison. Really, when someone says, "It's just as good as Sass?" tell then that they are a LIAR!
Regardless. Today, there are two different 'official' versions of Sass. The original Ruby version and the coming of age C port of Sass called libsass.
Ruby Sass comes packaged as a Gem. For those of you who don't know, Gems are packaged librarys for the Ruby language. To install the Sass Gem, run the following:
$ gem install sass
Of course this requires that you have Ruby installed on your computer. If you do not, then that is something that you need to address. THIS is why installing Sass is 'hard'. This is why you also hear things like, "We have to support Ruby to process CSS?"
On modern Macs, Ruby is already installed. For Windows, this is something that you have to address.
Depending on how your Mac is configured with Ruby, you may need to install as a super user by running:
$ sudo gem install sass
This will require a computer password.
Rails is a much more complicated eco system for developing web applications. Rails comes pre-configured with a asset management utility called the Asset Pipeline. Because of this pipeline and another technology called Sprockets, Sass needs a little help.
Rails comes pre-configures to use Sass, so in the generated Gemfile you should see a reference to
rails-sass. This is a wrapper for Sass in Rails that connects the pre-processor to Rails' Sprockets. You don't need to do much more then that,
rails-sass has a dependency to Sass and will import the Sass Gem for you.
Every other project on the planet that is not a Rails project will not natively support the original Ruby Sass. This has been a problem for years and one that many developers have struggled with.
To address this issue of application environment native support, libsass was born. libsass is written in C and so, with the proper wrapper, will be consumable by almost any development environment. At it's introduction, the creators of libsass wrote SassC, the C wrapper that will allow you to run a simple C app with libsass.
Once Node.js is installed, this typically comes bundled with npm, so we need to run the following:
$ npm install node-sass
npm supports deeply nested dependencies, so when you run this package install you will notice that libsass piggy backed in this and the whole C library is installed there for you.