sass-site/source/documentation/style-rules/declarations.md

title	table_of_contents	introduction
Property Declarations	true	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](/documentation/syntax/structure#expressions), which will be evaluated and included in the result.

{% codeExample 'declaration' %} .circle { $size: 100px; width: $size; height: $size; border-radius: $size * 0.5; }

.circle $size: 100px width: $size height: $size border-radius: $size * 0.5 {% endcodeExample %}

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!

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

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

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

#{$property}: $value

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

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.

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

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

}

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

&:hover
  font-size: 36px

{% endcodeExample %}

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.

{% codeExample 'nesting-shorthand' %} .info-page { margin: auto { bottom: 10px; top: 2px; } }

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

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.

{% codeExample 'hidden-declarations' %} $rounded-corners: false;

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

$rounded-corners: false

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

Custom Properties

{% compatibility 'dart: true', 'libsass: "3.5.0"', 'ruby: "3.5.0"', 'feature: "SassScript Syntax"' %} 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.

See the breaking change page for more details.

{% endcompatibility %}

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.

{% codeExample 'custom-properties' %} $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;

}

$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

{% endcodeExample %}

{% headsUp %} Unfortunately, interpolation removes quotes from strings, which makes it difficult to use quoted strings as values for custom properties when they come from Sass variables. As a workaround, you can use the meta.inspect() function to preserve the quotes.

{% codeExample 'custom-properties-strings-meta' %} @use "sass:meta";

$font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto;
$font-family-monospace: SFMono-Regular, Menlo, Monaco, Consolas;

:root {
  --font-family-sans-serif: #{meta.inspect($font-family-sans-serif)};
  --font-family-monospace: #{meta.inspect($font-family-monospace)};
}
===
@use "sass:meta"

$font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto
$font-family-monospace: SFMono-Regular, Menlo, Monaco, Consolas

:root
  --font-family-sans-serif: #{meta.inspect($font-family-sans-serif)}
  --font-family-monospace: #{meta.inspect($font-family-monospace)}

{% endcodeExample %} {% endheadsUp %}