Sass (stylesheet language)


Sass is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets. SassScript is the scripting language itself.
Sass consists of two syntaxes. The original syntax, called "the indented syntax," uses a syntax similar to Haml. It uses indentation to separate code blocks and newline characters to separate rules. The newer syntax, "SCSS", uses block formatting like that of CSS. It uses braces to denote code blocks and semicolons to separate rules within a block. The indented syntax and SCSS files are traditionally given the extensions.sass and.scss, respectively.
CSS3 consists of a series of selectors and pseudo-selectors that group rules that apply to them. Sass extends CSS by providing several mechanisms available in more traditional programming languages, particularly object-oriented languages, but that are not available to CSS3 itself. When SassScript is interpreted, it creates blocks of CSS rules for various selectors as defined by the Sass file. The Sass interpreter translates SassScript into CSS. Alternatively, Sass can monitor the.sass or.scss file and translate it to an output.css file whenever the.sass or.scss file is saved.
The indented syntax is a metalanguage. SCSS is a nested metalanguage, as valid CSS is valid SCSS with the same semantics.
SassScript provides the following mechanisms: variables, nesting, mixins, and selector inheritance.

History

Sass was initially designed by Hampton Catlin and developed by Natalie Weizenbaum. After its initial versions, Weizenbaum and Chris Eppstein have continued to extend Sass with SassScript, a scripting language used in Sass files.

Major implementations

SassScript was implemented in multiple languages, the noteworthy implementations are:

Variables

Sass allows variables to be defined. Variables begin with a dollar sign. Variable assignment is done with a colon.
SassScript supports four data types:
Variables can be arguments to or results from one of several available functions. During translation, the values of the variables are inserted into the output CSS document.
SCSSSassCompiled CSS

$primary-color: #3bbfce;
$margin: 16px;
.content-navigation
.border

$primary-color: #3bbfce
$margin: 16px
.content-navigation
border-color: $primary-color
color: darken
.border
padding: $margin/2
margin: $margin/2
border-color: $primary-color

.content-navigation
.border

Nesting

CSS does support logical nesting, but the code blocks themselves are not nested. Sass allows the nested code to be inserted within each other.
SCSSSassCompiled CSS

table.hl
li

table.hl
margin: 2em 0
td.ln
text-align: right

li
font:
family: serif
weight: bold
size: 1.3em

table.hl
table.hl td.ln
li

More complicated types of nesting including namespace nesting and parent references are discussed in the Sass documentation.
SCSSSassCompiled CSS

@mixin table-base
  1. data

=table-base
th
text-align: center
font-weight: bold
td, th
padding: 2px
  1. data
+table-base

  1. data th
  2. data td, #data th

Loops

Sass allows for iterating over variables using, and, which can be used to apply different styles to elements with similar classes or ids.
SassCompiled CSS

$squareCount: 4
@for $i from 1 through $squareCount
#square-#
background-color: red
width: 50px * $i
height: 120px / $i

  1. square-1
  2. square-2
  3. square-3

Arguments

Mixins also support arguments.
SassCompiled CSS

=left
float: left
margin-left: $dist
  1. data
+left

  1. data

In combination

SassCompiled CSS

=table-base
th
text-align: center
font-weight: bold
td, th
padding: 2px
=left
float: left
margin-left: $dist
  1. data
+left
+table-base

  1. data
  2. data th
  3. data td, #data th

Selector inheritance

While CSS3 supports the Document Object Model hierarchy, it does not allow selector inheritance. In Sass, inheritance is achieved by inserting a line inside of a code block that uses the @extend keyword and references another selector. The extended selector's attributes are applied to the calling selector.
SassCompiled CSS

.error
border: 1px #f00
background: #fdd
.error.intrusion
font-size: 1.3em
font-weight: bold
.badError
@extend.error
border-width: 3px

.error,.badError
.error.intrusion,
.badError.intrusion
.badError

Sass supports multiple inheritance.

libSass

At the 2012 HTML5 Developer Conference, Hampton Catlin, the creator of Sass, announced version 1.0 of libSass, an open source C++ implementation of Sass developed by Catlin, Aaron Leung, and the engineering team at Moovweb. Current Sass maintainer, Chris Eppstein, has expressed intent to contribute as well.
According to Catlin, libSass can be "drop into anything and it will have Sass in it...You could drop it right into Firefox today and build Firefox and it will compile in there. We wrote our own parser from scratch to make sure that would be possible."
The design goals of libSass are: