Sass is a stylesheet language that’s compiled to CSS. It allows you to use variables, nested rules, mixins, functions, and more, all with a fully CSS-compatible syntax. Sass helps keep large stylesheets well-organized and makes it easy to share design within and across projects.

• Sass facilitates you to write clean, easy and less CSS in a programming construct.
• It contains fewer codes so you can write CSS quicker.
• It is more stable, powerful, and elegant because it is an extension of CSS. So, it is easy for designers and developers to work more efficiently and quickly.
• It is compatible with all versions of CSS. So, you can use any available CSS libraries.
• It provides nesting so you can use nested syntax and useful functions like color manipulation, math functions and other values.

What You Should Already Know

Before you continue you should have a basic understanding of the following:

• HTML
• CSS

When you install Sass on the command line, you'll be able to run the sass executable to compile .sass and .scss files to .css files. For example:

sass source/stylesheets/index.scss build/stylesheets/index.css

Install Anywhere (Standalone)

You can install Sass on Windows, Mac, or Linux by downloading the package for your operating system from GitHub and adding it to your PATH. That’s all—there are no external dependencies and nothing else you need to install.

Install Anywhere (npm)

If you use Node.js, you can also install Sass using npm by running

npm install -g sass

However, please note that this will install the pure JavaScript implementation of Sass, which runs somewhat slower than the other options listed here. But it has the same interface, so it’ll be easy to swap in another implementation later if you need a bit more speed!

CSS on its own can be fun, but stylesheets are getting larger, more complex, and harder to maintain. This is where a preprocessor can help. Sass lets you use features that don't exist in CSS yet like variables, nesting, mixins, inheritance and other nifty goodies that make writing CSS fun again.

Once you start tinkering with Sass, it will take your preprocessed Sass file and save it as a normal CSS file that you can use in your website.

The most direct way to make this happen is in your terminal. Once Sass is installed, you can compile your Sass to CSS using the sass command. You'll need to tell Sass which file to build from, and where to output CSS to. For example, running sass input.scss output.css from your terminal would take a single Sass file, input.scss, and compile that file to output.css.

You can also watch individual files or directories with the --watch flag. The watch flag tells Sass to watch your source files for changes, and re-compile CSS each time you save your Sass. If you wanted to watch (instead of manually build) your input.scss file, you'd just add the watch flag to your command, like so:

sass --watch input.scss output.css

You can watch and output to directories by using folder paths as your input and output, and separating them with a colon. In this example:

sass --watch app/sass:public/stylesheets

Sass would watch all files in the app/sass folder for changes, and compile CSS to the public/stylesheets folder.

Think of variables as a way to store information that you want to reuse throughout your stylesheet. You can store things like colors, font stacks, or any CSS value you think you'll want to reuse. Sass uses the $ symbol to make something a variable. Here's an example:

SASS

$font-stack:    Helvetica, sans-serif
$primary-color: #333
              
body
  font: 100% $font-stack
  color: $primary-color

CSS

body {
  font: 100% Helvetica, sans-serif;
  color: #333;
} 

When the Sass is processed, it takes the variables we define for the $font-stack and $primary-color and outputs normal CSS with our variable values placed in the CSS. This can be extremely powerful when working with brand colors and keeping them consistent throughout the site.

You can create partial Sass files that contain little snippets of CSS that you can include in other Sass files. This is a great way to modularize your CSS and help keep things easier to maintain. A partial is a Sass file named with a leading underscore. You might name it something like _partial.scss. The underscore lets Sass know that the file is only a partial file and that it should not be generated into a CSS file. Sass partials are used with the @use rule.

You don't have to write all your Sass in a single file. You can split it up however you want with the @use rule. This rule loads another Sass file as a module, which means you can refer to its variables, mixins, and functions in your Sass file with a namespace based on the filename. Using a file will also include the CSS it generates in your compiled output!

SASS

// _base.sass
$font-stack:    Helvetica, sans-serif
$primary-color: #333

body
  font: 100% $font-stack
  color: $primary-color

// styles.sass
@use 'base'

.inverse
  background-color: base.$primary-color
  color: white

CSS

body {
  font: 100% Helvetica, sans-serif;
  color: #333; 
}
              
.inverse {
  background-color: #333;
  color: white;
}

Notice we're using @use 'base'; in the styles.scss file. When you use a file you don't need to include the file extension. Sass is smart and will figure it out for you.

Some things in CSS are a bit tedious to write, especially with CSS3 and the many vendor prefixes that exist. A mixin lets you make groups of CSS declarations that you want to reuse throughout your site. You can even pass in values to make your mixin more flexible. A good use of a mixin is for vendor prefixes. Here's an example for transform.

SASS

=transform($property)
  -webkit-transform: $property
  -ms-transform: $property
  transform: $property

.box
  +transform(rotate(30deg))

CSS

.box {
  -webkit-transform: rotate(30deg);
  -ms-transform: rotate(30deg);
  transform: rotate(30deg);
}

To create a mixin you use the @mixin directive and give it a name. We've named our mixin transform. We're also using the variable $property inside the parentheses so we can pass in a transform of whatever we want. After you create your mixin, you can then use it as a CSS declaration starting with @include followed by the name of the mixin.

This is one of the most useful features of Sass. Using @extend lets you share a set of CSS properties from one selector to another. It helps keep your Sass very DRY. In our example we're going to create a simple series of messaging for errors, warnings and successes using another feature which goes hand in hand with extend, placeholder classes. A placeholder class is a special type of class that only prints when it is extended, and can help keep your compiled CSS neat and clean.

SASS

/* This CSS will print because %message-shared is extended. */
%message-shared
  border: 1px solid #ccc
  padding: 10px
  color: #333

// This CSS won't print because %equal-heights is never extended.
%equal-heights
  display: flex
  flex-wrap: wrap

.message
  @extend %message-shared

.success
  @extend %message-shared
  border-color: green

.error
  @extend %message-shared
  border-color: red

.warning
  @extend %message-shared
  border-color: yellow

Doing math in your CSS is very helpful. Sass has a handful of standard math operators like +, -, *, /, and %. In our example we're going to do some simple math to calculate widths for an aside & article.

SASS

.container
  width: 100%

article[role="main"]
  float: left
  width: 600px / 960px * 100%

aside[role="complementary"]
  float: right
  width: 300px / 960px * 100%

CSS

.container {
  width: 100%;
}
              
article[role="main"] {
  float: left;
  width: 62.5%;
}
              
aside[role="complementary"] {
  float: right;
  width: 31.25%;
}

We've created a very simple fluid grid, based on 960px. Operations in Sass let us do something like take pixel values and convert them to percentages without much hassle.