Property Declarations

In Sass as in CSS, property declarations define how elements that match a selector are styled. But Sass adds extra features to make them easier to write and to automate. First and foremost, a declaration's value can be any SassScript expression, which will be evaluated and included in the result.

SCSS Syntax

.circle {
  $size: 100px;
  width: $size;
  height: $size;
  border-radius: $size / 2;
}

Sass Syntax

.circle
  $size: 100px
  width: $size
  height: $size
  border-radius: $size / 2

CSS Output

.circle {
  width: 100px;
  height: 100px;
  border-radius: 50px;
}

Interpolation

A property’s name can include interpolation, which makes it possible to dynamically generate properties as needed. You can even interpolate the entire property name!

SCSS Syntax

@mixin prefix($property, $value, $prefixes) {
  @each $prefix in $prefixes {
    -#{$prefix}-#{$property}: $value;
  }
  #{$property}: $value;
}

.gray {
  @include prefix(filter, grayscale(50%), moz webkit);
}

Sass Syntax

@mixin prefix($property, $value, $prefixes)
  @each $prefix in $prefixes
    -#{$prefix}-#{$property}: $value

  #{$property}: $value


.gray
  @include prefix(filter, grayscale(50%), moz webkit)

CSS Output

.gray {
  -moz-filter: grayscale(50%);
  -webkit-filter: grayscale(50%);
  filter: grayscale(50%);
}





Nesting

Many CSS properties start with the same prefix that acts as a kind of namespace. For example, font-family, font-size, and font-weight all start with font-. Sass makes this easier and less redundant by allowing property declarations to be nested. The outer property names are added to the inner, separated by a hyphen.

SCSS Syntax

.enlarge {
  font-size: 14px;
  transition: {
    property: font-size;
    duration: 4s;
    delay: 2s;
  }

  &:hover { font-size: 36px; }
}

Sass Syntax

.enlarge
  font-size: 14px
  transition:
    property: font-size
    duration: 4s
    delay: 2s

  &:hover
    font-size: 36px

CSS Output

.enlarge {
  font-size: 14px;
  transition-property: font-size;
  transition-duration: 4s;
  transition-delay: 2s;
}
.enlarge:hover {
  font-size: 36px;
}

Some of these CSS properties have shorthand versions that use the namespace as the property name. For these, you can write both the shorthand value and the more explicit nested versions.

SCSS Syntax

.info-page {
  margin: auto {
    bottom: 10px;
    top: 2px;
  }
}

Sass Syntax

.info-page
  margin: auto
    bottom: 10px
    top: 2px


CSS Output

.info-page {
  margin: auto;
  margin-bottom: 10px;
  margin-top: 2px;
}

Hidden Declarations

Sometimes you only want a property declaration to show up some of the time. If a declaration’s value is null or an empty unquoted string, Sass won’t compile that declaration to CSS at all.

SCSS Syntax

$rounded-corners: false;

.button {
  border: 1px solid black;
  border-radius: if($rounded-corners, 5px, null);
}

Sass Syntax

$rounded-corners: false

.button
  border: 1px solid black
  border-radius: if($rounded-corners, 5px, null)

CSS Output

.button {
  border: 1px solid black;
}



Custom Properties

Compatibility (SassScript Syntax):
Dart Sass
LibSass
since 3.5.0
Ruby Sass
since 3.5.0

Older versions of LibSass and Ruby Sass parsed custom property declarations just like any other property declaration, allowing the full range of SassScript expressions as values. Even when using these versions, it’s recommended that you use interpolation to inject SassScript values for forwards-compatibility.

CSS custom properties, also known as CSS variables, have an unusual declaration syntax: they allow almost any text at all in their declaration values. What’s more, those values are accessible to JavaScript, so any value might potentially be relevant to the user. This includes values that would normally be parsed as SassScript.

Because of this, Sass parses custom property declarations differently than other property declarations. All tokens, including those that look like SassScript, are passed through to CSS as-is. The only exception is interpolation, which is the only way to inject dynamic values into a custom property.

SCSS Syntax

$primary: #81899b;
$accent: #302e24;
$warn: #dfa612;

:root {
  --primary: #{$primary};
  --accent: #{$accent};
  --warn: #{$warn};

  // Even though this looks like a Sass variable, it's valid CSS so it's not
  // evaluated.
  --consumed-by-js: $primary;
}

Sass Syntax

$primary: #81899b
$accent: #302e24
$warn: #dfa612

:root
  --primary: #{$primary}
  --accent: #{$accent}
  --warn: #{$warn}

  // Even though this looks like a Sass variable, it's valid CSS so it's not
  // evaluated.
  --consumed-by-js: $primary

CSS Output

:root {
  --primary: #81899b;
  --accent: #302e24;
  --warn: #dfa612;
  --consumed-by-js: $primary;
}