sass-site/source/documentation/style-rules/declarations.liquid
2023-06-21 17:03:14 -04:00

232 lines
6.4 KiB
Plaintext

---
title: Property Declarations
table_of_contents: true
introduction: >
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: $size * 0.5
{% endcodeExample %}
{% markdown %}
## Interpolation
A property's name can include [interpolation][], which makes it possible to
dynamically generate properties as needed. You can even interpolate the entire
property name!
[interpolation]: /documentation/interpolation
{% endmarkdown %}
{% codeExample 'interpolation' %}
@mixin prefix($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 %}
{% markdown %}
## 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.
{% endmarkdown %}
{% 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 %}
{% markdown %}
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.
{% endmarkdown %}
{% codeExample 'nesting-shorthand' %}
.info-page {
margin: auto {
bottom: 10px;
top: 2px;
}
}
===
.info-page
margin: auto
bottom: 10px
top: 2px
{% endcodeExample %}
{% markdown %}
## 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.
[`null`]: /documentation/values/null
[unquoted string]: /documentation/values/strings#unquoted
{% endmarkdown %}
{% 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 %}
{% markdown %}
## 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.
[the breaking change page]: /documentation/breaking-changes/css-vars
{% 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.
[CSS Custom Properties]: https://developer.mozilla.org/en-US/docs/Web/CSS/--*
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.
[interpolation]: /documentation/interpolation
{% endmarkdown %}
{% 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 false %}
{% markdown %}
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.
[interpolation]: /documentation/interpolation
[`meta.inspect()` function]: /documentation/modules/meta#inspect
{% endmarkdown %}
{% 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 %}