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232 lines
6.4 KiB
Plaintext
232 lines
6.4 KiB
Plaintext
---
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title: Property Declarations
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table_of_contents: true
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introduction: >
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In Sass as in CSS, property declarations define how elements that match a
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selector are styled. But Sass adds extra features to make them easier to write
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and to automate. First and foremost, a declaration's value can be any
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[SassScript expression](/documentation/syntax/structure#expressions), which
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will be evaluated and included in the result.
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---
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{% codeExample 'declaration' %}
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.circle {
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$size: 100px;
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width: $size;
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height: $size;
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border-radius: $size * 0.5;
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}
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===
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.circle
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$size: 100px
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width: $size
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height: $size
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border-radius: $size * 0.5
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{% endcodeExample %}
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{% markdown %}
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## Interpolation
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A property's name can include [interpolation][], which makes it possible to
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dynamically generate properties as needed. You can even interpolate the entire
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property name!
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[interpolation]: /documentation/interpolation
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{% endmarkdown %}
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{% codeExample 'interpolation' %}
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@mixin prefix($property, $value, $prefixes) {
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@each $prefix in $prefixes {
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-#{$prefix}-#{$property}: $value;
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}
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#{$property}: $value;
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}
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.gray {
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@include prefix(filter, grayscale(50%), moz webkit);
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}
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===
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@mixin prefix($property, $value, $prefixes)
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@each $prefix in $prefixes
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-#{$prefix}-#{$property}: $value
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#{$property}: $value
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.gray
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@include prefix(filter, grayscale(50%), moz webkit)
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{% endcodeExample %}
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{% markdown %}
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## Nesting
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Many CSS properties start with the same prefix that acts as a kind of
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namespace. For example, `font-family`, `font-size`, and `font-weight` all
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start with `font-`. Sass makes this easier and less redundant by allowing
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property declarations to be nested. The outer property names are added to the
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inner, separated by a hyphen.
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{% endmarkdown %}
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{% codeExample 'nesting' %}
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.enlarge {
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font-size: 14px;
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transition: {
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property: font-size;
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duration: 4s;
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delay: 2s;
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}
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&:hover { font-size: 36px; }
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}
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===
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.enlarge
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font-size: 14px
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transition:
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property: font-size
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duration: 4s
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delay: 2s
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&:hover
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font-size: 36px
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{% endcodeExample %}
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{% markdown %}
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Some of these CSS properties have shorthand versions that use the namespace as
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the property name. For these, you can write both the shorthand value *and* the
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more explicit nested versions.
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{% endmarkdown %}
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{% codeExample 'nesting-shorthand' %}
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.info-page {
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margin: auto {
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bottom: 10px;
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top: 2px;
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}
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}
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===
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.info-page
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margin: auto
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bottom: 10px
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top: 2px
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{% endcodeExample %}
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{% markdown %}
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## Hidden Declarations
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Sometimes you only want a property declaration to show up some of the time. If
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a declaration's value is [`null`][] or an empty [unquoted string][], Sass
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won't compile that declaration to CSS at all.
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[`null`]: /documentation/values/null
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[unquoted string]: /documentation/values/strings#unquoted
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{% endmarkdown %}
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{% codeExample 'hidden-declarations' %}
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$rounded-corners: false;
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.button {
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border: 1px solid black;
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border-radius: if($rounded-corners, 5px, null);
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}
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===
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$rounded-corners: false
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.button
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border: 1px solid black
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border-radius: if($rounded-corners, 5px, null)
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{% endcodeExample %}
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{% markdown %}
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## Custom Properties
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{% compatibility 'dart: true', 'libsass: "3.5.0"', 'ruby: "3.5.0"', 'feature: "SassScript Syntax"' %}
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Older versions of LibSass and Ruby Sass parsed custom property declarations
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just like any other property declaration, allowing the full range of
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SassScript expressions as values. Even when using these versions, it's
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recommended that you use interpolation to inject SassScript values for
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forwards-compatibility.
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See [the breaking change page][] for more details.
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[the breaking change page]: /documentation/breaking-changes/css-vars
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{% endcompatibility %}
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[CSS custom properties][], also known as CSS variables, have an unusual
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declaration syntax: they allow almost any text at all in their declaration
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values. What's more, those values are accessible to JavaScript, so any value
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might potentially be relevant to the user. This includes values that would
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normally be parsed as SassScript.
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[CSS Custom Properties]: https://developer.mozilla.org/en-US/docs/Web/CSS/--*
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Because of this, Sass parses custom property declarations differently than
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other property declarations. All tokens, including those that look like
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SassScript, are passed through to CSS as-is. The only exception is
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[interpolation][], which is the only way to inject dynamic values into a
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custom property.
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[interpolation]: /documentation/interpolation
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{% endmarkdown %}
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{% codeExample 'custom-properties' %}
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$primary: #81899b;
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$accent: #302e24;
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$warn: #dfa612;
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:root {
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--primary: #{$primary};
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--accent: #{$accent};
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--warn: #{$warn};
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// Even though this looks like a Sass variable, it's valid CSS so it's not
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// evaluated.
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--consumed-by-js: $primary;
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}
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===
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$primary: #81899b
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$accent: #302e24
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$warn: #dfa612
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:root
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--primary: #{$primary}
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--accent: #{$accent}
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--warn: #{$warn}
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// Even though this looks like a Sass variable, it's valid CSS so it's not
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// evaluated.
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--consumed-by-js: $primary
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{% endcodeExample %}
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{% headsUp false %}
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{% markdown %}
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Unfortunately, [interpolation][] removes quotes from strings, which makes it
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difficult to use quoted strings as values for custom properties when they
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come from Sass variables. As a workaround, you can use the [`meta.inspect()`
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function][] to preserve the quotes.
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[interpolation]: /documentation/interpolation
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[`meta.inspect()` function]: /documentation/modules/meta#inspect
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{% endmarkdown %}
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{% codeExample 'custom-properties-strings-meta' %}
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@use "sass:meta";
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$font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto;
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$font-family-monospace: SFMono-Regular, Menlo, Monaco, Consolas;
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:root {
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--font-family-sans-serif: #{meta.inspect($font-family-sans-serif)};
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--font-family-monospace: #{meta.inspect($font-family-monospace)};
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}
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===
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@use "sass:meta"
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$font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto
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$font-family-monospace: SFMono-Regular, Menlo, Monaco, Consolas
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:root
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--font-family-sans-serif: #{meta.inspect($font-family-sans-serif)}
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--font-family-monospace: #{meta.inspect($font-family-monospace)}
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{% endcodeExample %}
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{% endheadsUp %}
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