Sass Basics

Before you can use Sass, you need to set it up on your project. If you want to just browse here, go ahead, but we recommend you go install Sass first. Go here if you want to learn how to get everything set up.

PreprocessingPreprocessing permalink

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 has features that don’t exist in CSS yet like nesting, mixins, inheritance, and other nifty goodies that help you write robust, maintainable CSS.

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.

💡 Fun fact:

Sass has two syntaxes! The SCSS syntax (.scss) is used most commonly. It’s a superset of CSS, which means all valid CSS is also valid SCSS. The indented syntax (.sass) is more unusual: it uses indentation rather than curly braces to nest statements, and newlines instead of semicolons to separate them. All our examples are available in both syntaxes.

VariablesVariables permalink

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:

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    SCSS Syntax$font-stack: Helvetica, sans-serif;
$primary-color: #333;

body {
  font: 100% $font-stack;
  color: $primary-color;
}

      
      Playground
    Sass Syntax$font-stack: Helvetica, sans-serif
$primary-color: #333

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

CSS Outputbody {
  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.

NestingNesting permalink

When writing HTML you’ve probably noticed that it has a clear nested and visual hierarchy. CSS, on the other hand, doesn’t.

Sass will let you nest your CSS selectors in a way that follows the same visual hierarchy of your HTML. Be aware that overly nested rules will result in over-qualified CSS that could prove hard to maintain and is generally considered bad practice.

With that in mind, here’s an example of some typical styles for a site’s navigation:

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    SCSS Syntaxnav {
  ul {
    margin: 0;
    padding: 0;
    list-style: none;
  }

  li { display: inline-block; }

  a {
    display: block;
    padding: 6px 12px;
    text-decoration: none;
  }
}

      
      Playground
    Sass Syntaxnav
  ul
    margin: 0
    padding: 0
    list-style: none

  li
    display: inline-block

  a
    display: block
    padding: 6px 12px
    text-decoration: none


CSS Outputnav ul {
  margin: 0;
  padding: 0;
  list-style: none;
}
nav li {
  display: inline-block;
}
nav a {
  display: block;
  padding: 6px 12px;
  text-decoration: none;
}

You’ll notice that the ul, li, and a selectors are nested inside the nav selector. This is a great way to organize your CSS and make it more readable.

PartialsPartials permalink

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.

ModulesModules permalink

Dart Sass: since 1.23.0
LibSass: ✗
Ruby Sass: ✗

Only Dart Sass currently supports @use. Users of other implementations must use the @import rule instead.

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!

  SCSS

  Sass

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SCSS Syntax// _base.scss
$font-stack: Helvetica, sans-serif;
$primary-color: #333;

body {
  font: 100% $font-stack;
  color: $primary-color;
}
// styles.scss
@use 'base';

.inverse {
  background-color: base.$primary-color;
  color: white;
}
Sass Syntax// _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 Outputbody {
  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.

MixinsMixins permalink

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. It helps keep your Sass very DRY. You can even pass in values to make your mixin more flexible. Here’s an example for theme.

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    SCSS Syntax@mixin theme($theme: DarkGray) {
  background: $theme;
  box-shadow: 0 0 1px rgba($theme, .25);
  color: #fff;
}

.info {
  @include theme;
}
.alert {
  @include theme($theme: DarkRed);
}
.success {
  @include theme($theme: DarkGreen);
}



      
      Playground
    Sass Syntax@mixin theme($theme: DarkGray)
  background: $theme
  box-shadow: 0 0 1px rgba($theme, .25)
  color: #fff

.info
  @include theme

.alert
  @include theme($theme: DarkRed)

.success
  @include theme($theme: DarkGreen)




CSS Output.info {
  background: DarkGray;
  box-shadow: 0 0 1px rgba(169, 169, 169, 0.25);
  color: #fff;
}

.alert {
  background: DarkRed;
  box-shadow: 0 0 1px rgba(139, 0, 0, 0.25);
  color: #fff;
}

.success {
  background: DarkGreen;
  box-shadow: 0 0 1px rgba(0, 100, 0, 0.25);
  color: #fff;
}

To create a mixin you use the @mixin directive and give it a name. We’ve named our mixin theme. We’re also using the variable $theme inside the parentheses so we can pass in a theme 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.

Extend/InheritanceExtend/Inheritance permalink

Using @extend lets you share a set of CSS properties from one selector to another. 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.

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      Playground
    SCSS Syntax/* 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;
}

      
      Playground
    Sass Syntax/* 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






CSS Output/* This CSS will print because %message-shared is extended. */
.warning, .error, .success, .message {
  border: 1px solid #ccc;
  padding: 10px;
  color: #333;
}

.success {
  border-color: green;
}

.error {
  border-color: red;
}

.warning {
  border-color: yellow;
}

What the above code does is tells .message, .success, .error, and .warning to behave just like %message-shared. That means anywhere that %message-shared shows up, .message, .success, .error, & .warning will too. The magic happens in the generated CSS, where each of these classes will get the same CSS properties as %message-shared. This helps you avoid having to write multiple class names on HTML elements.

You can extend most simple CSS selectors in addition to placeholder classes in Sass, but using placeholders is the easiest way to make sure you aren’t extending a class that’s nested elsewhere in your styles, which can result in unintended selectors in your CSS.

Note that the CSS in %equal-heights isn’t generated, because %equal-heights is never extended.

OperatorsOperators permalink

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

  SCSS

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    SCSS Syntax@use "sass:math";

.container {
  display: flex;
}

article[role="main"] {
  width: math.div(600px, 960px) * 100%;
}

aside[role="complementary"] {
  width: math.div(300px, 960px) * 100%;
  margin-left: auto;
}

      
      Playground
    Sass Syntax@use "sass:math"

.container
  display: flex

article[role="main"]
  width: math.div(600px, 960px) * 100%

aside[role="complementary"]
  width: math.div(300px, 960px) * 100%
  margin-left: auto



CSS Output.container {
  display: flex;
}

article[role=main] {
  width: 62.5%;
}

aside[role=complementary] {
  width: 31.25%;
  margin-left: auto;
}

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.