---
layout: has_navigation
title: Sass Basics
introduction: >
  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](/install) if you want to learn how to get everything set up.
navigation: |
  ### Topics

  <nav class="sl-c-list-navigation-wrapper">

  - [Preprocessing](#preprocessing)
  - [Variables](#variables)
  - [Nesting](#nesting)
  - [Partials](#partials)
  - [Modules](#modules)
  - [Mixins](#mixins)
  - [Inheritance](#inheritance)
  - [Operators](#operators)

  </nav>
---

<section id="preprocessing">
{% # retain older link %}
<span id="topic-1"></span>

{% markdown %}
## Preprocessing

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:

```shell
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:

```shell
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.
{% endmarkdown %}

{% funFact %}
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.
{% endfunFact %}

</section>

<hr>

<section id="variables">
{% # retain older link %}
<span id="topic-2"></span>

{% markdown %}
## Variables

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:
{% endmarkdown %}

{% codeExample 'variables' %}
$font-stack: Helvetica, sans-serif;
$primary-color: #333;

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

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

{% markdown %}
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.
{% endmarkdown %}

</section>

<hr>

<section id="nesting">
{% # retain older link %}
<span id="topic-3"></span>

{% markdown %}
## Nesting

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:
{% endmarkdown %}

{% codeExample 'nesting' %}
nav {
  ul {
    margin: 0;
    padding: 0;
    list-style: none;
  }

  li { display: inline-block; }

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

  li
    display: inline-block

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

{% markdown %}
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.
{% endmarkdown %}

</section>

<hr>

<section id="partials">
{% # retain older link %}
<span id="topic-4"></span>

{% markdown %}
## Partials

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.
{% endmarkdown %}

</section>

<hr>

<section id="modules">
{% # retain older link %}
<span id="topic-5"></span>

{{ '## Modules' | markdown }}

{% render 'documentation/snippets/module-system-status' %}

{% markdown %}
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!

[mixins]: #mixins
[functions]: documentation/at-rules/function
{% endmarkdown %}

{% codeExample 'modules' %}
// _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;
}
===
// _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
===
body {
  font: 100% Helvetica, sans-serif;
  color: #333;
}

.inverse {
  background-color: #333;
  color: white;
}
{% endcodeExample %}

{% markdown %}
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.
{% endmarkdown %}

</section>

<hr>

<section id="mixins">
{% # retain older link %}
<span id="topic-6"></span>

{% markdown %}
## Mixins

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`.
{% endmarkdown %}

{% codeExample 'mixins' %}
@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);
}
===
@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)
{% endcodeExample %}

{% markdown %}
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.
{% endmarkdown %}

</section>

<hr>

<section id="inheritance">
{% # retain older link %}
<span id="topic-7"></span>

{% markdown %}
## Extend/Inheritance

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.
{% endmarkdown %}

{% codeExample 'extend-inheritance' %}
/* 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;
}
===
/* 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
{% endcodeExample %}

{% markdown %}
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.
{% endmarkdown %}

</section>

<hr>

<section id="operators">
{% # retain older link %}
<span id="topic-8"></span>

{% markdown %}
## Operators

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`.
{% endmarkdown %}

{% codeExample 'operators' %}
@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;
}
===
@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
===
.container {
  display: flex;
}

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

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

{% markdown %}
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.
{% endmarkdown %}

</section>