source/documentation/at-rules/import.md
Sass imports have the same syntax as CSS imports, except that they allow
multiple imports to be separated by commas rather than requiring each one to
have its own @import. Also, in the indented syntax, imported URLs aren't
required to have quotes.
{% headsUp %}
As of Dart Sass 1.80.0, the @import rule is deprecated and will be removed
from the language in Dart Sass 3.0.0. Prefer the @use rule instead.
The @import rule has a number of serious issues:
@import makes all variables, mixins, and functions globally accessible.
This makes it very difficult for people (or tools) to tell where anything is
defined.
Because everything's global, libraries must add a prefix to all their members to avoid naming collisions.
@extend rules are also global, which makes it difficult to predict
which style rules will be extended.
Each stylesheet is executed and its CSS emitted every time it's
@imported, which increases compilation time and produces bloated output.
There was no way to define private members or placeholder selectors that were inaccessible to downstream stylesheets.
The new module system and the @use rule address all these problems.
We've written a migration tool that automatically converts most
@import-based code to @use-based code in a flash. Just point it at your
entrypoints and let it run!
{% endheadsUp %}
// foundation/_lists.scss ul, ol { text-align: left;
& & {
padding: {
bottom: 0;
left: 0;
}
}
// foundation/_lists.sass ul, ol text-align: left
& &
padding:
bottom: 0
left: 0
code { padding: .25em; line-height: 0; }
ul, ol { text-align: left; } ul ul, ol ol { padding-bottom: 0; padding-left: 0; } {% endcodeExample %}
When Sass imports a file, that file is evaluated as though its contents appeared
directly in place of the @import. Any mixins, functions, and
variables from the imported file are made available, and all its CSS is
included at the exact point where the @import was written. What's more, any
mixins, functions, or variables that were defined before the @import
(including from other @imports) are available in the imported stylesheet.
{% headsUp %} If the same stylesheet is imported more than once, it will be evaluated again each time. If it just defines functions and mixins, this usually isn't a big deal, but if it contains style rules they'll be compiled to CSS more than once. {% endheadsUp %}
It wouldn't be any fun to write out absolute URLs for every stylesheet you
import, so Sass's algorithm for finding a file to import makes it a little
easier. For starters, you don't have to explicitly write out the extension of
the file you want to import; @import "variables" will automatically load
variables.scss, variables.sass, or variables.css.
{% headsUp %} To ensure that stylesheets work on every operating system, Sass imports files by URL, not by file path. This means you need to use forward slashes, not backslashes, even when you're on Windows. {% endheadsUp %}
All Sass implementations allow users to provide load paths: paths on the
filesystem that Sass will look in when resolving imports. For example, if you
pass node_modules/susy/sass as a load path, you can use @import "susy" to
load node_modules/susy/sass/susy.scss.
Imports will always be resolved relative to the current file first, though. Load paths will only be used if no relative file exists that matches the import. This ensures that you can't accidentally mess up your relative imports when you add a new library.
{% funFact %}
Unlike some other languages, Sass doesn't require that you use ./ for
relative imports. Relative imports are always available.
{% endfunFact %}
As a convention, Sass files that are only meant to be imported, not compiled on
their own, begin with _ (as in _code.scss). These are called partials, and
they tell Sass tools not to try to compile those files on their own. You can
leave off the _ when importing a partial.
{% compatibility 'dart: true', 'libsass: "3.6.0"', 'ruby: "3.6.0"' %}{% endcompatibility %}
If you write an _index.scss or _index.sass in a folder, when the folder
itself is imported that file will be loaded in its place.
// foundation/_lists.scss ul, ol { text-align: left;
& & {
padding: {
bottom: 0;
left: 0;
}
}
// foundation/_lists.sass ul, ol text-align: left
& &
padding:
bottom: 0
left: 0
code { padding: .25em; line-height: 0; }
ul, ol { text-align: left; } ul ul, ol ol { padding-bottom: 0; padding-left: 0; } {% endcodeExample %}
All Sass implementations provide a way to define custom importers, which control
how @imports locate stylesheets:
Node Sass and Dart Sass on npm provide an importer option as
part of their JS API.
Dart Sass on pub provides an abstract Importer class that can be
extended by a custom importer.
Ruby Sass provides an abstract Importers::Base class that can be
extended by a custom importer.
Imports are usually written at the top level of a stylesheet, but they don't have to be. They can nested within style rules or plain CSS at-rules as well. The imported CSS is nested in that context, which makes nested imports useful for scoping a chunk of CSS to a particular element or media query. Top-level mixins, functions, and variables defined in the nested import are only available in the nested context.
.theme-sample pre, .theme-sample code { font-family: 'Source Code Pro', Helvetica, Arial; border-radius: 4px; } {% endcodeExample %}
{% funFact %} Nested imports are very useful for scoping third-party stylesheets, but if you're the author of the stylesheet you're importing, it's usually a better idea to write your styles in a mixin and include that mixin in the nested context. A mixin can be used in more flexible ways, and it's clearer when looking at the imported stylesheet how it's intended to be used.
{% endfunFact %}
{% headsUp %} The CSS in nested imports is evaluated like a mixin, which means that any parent selectors will refer to the selector in which the stylesheet is nested.
{% codeExample 'parent-selector' %} // _theme.scss ul li { $padding: 16px; padding-left: $padding; [dir=rtl] & { padding: { left: 0; right: $padding; } } } --- // style.scss .theme-sample { @import "theme"; } === // _theme.sass ul li $padding: 16px padding-left: $padding [dir=rtl] & padding: left: 0 right: $padding --- // style.sass .theme-sample @import theme === .theme-sample ul li { padding-left: 16px; } [dir=rtl] .theme-sample ul li { padding-left: 0; padding-right: 16px; } {% endcodeExample %} {% endheadsUp %}
{% compatibility 'dart: "1.11.0"', 'libsass: "partial"', 'ruby: false' %}
LibSass supports importing files with the extension .css, but contrary to
the specification they're treated as SCSS files rather than being parsed as
CSS. This behavior has been deprecated, and an update is in the works to
support the behavior described below.
{% endcompatibility %}
In addition to importing .sass and .scss files, Sass can import plain old
.css files. The only rule is that the import must not explicitly include the
.css extension, because that's used to indicate a plain CSS @import.
code { padding: .25em; line-height: 0; } {% endcodeExample %}
CSS files imported by Sass don't allow any special Sass features. In order to make sure authors don't accidentally write Sass in their CSS, all Sass features that aren't also valid CSS will produce errors. Otherwise, the CSS will be rendered as-is. It can even be extended!
@imports{% compatibility 'dart: true', 'libsass: "partial"', 'ruby: true' %}
By default, LibSass handles plain CSS imports correctly. However, any custom
importers will incorrectly apply to plain-CSS @import rules, making it
possible for those rules to load Sass files.
{% endcompatibility %}
Because @import is also defined in CSS, Sass needs a way of compiling plain
CSS @imports without trying to import the files at compile time. To accomplish
this, and to ensure SCSS is as much of a superset of CSS as possible, Sass will
compile any @imports with the following characteristics to plain CSS imports:
.css.http:// or https://.url().@import "theme.css" @import "http://fonts.googleapis.com/css?family=Droid+Sans" @import url(theme) @import "landscape" screen and (orientation: landscape) {% endcodeExample %}
Although Sass imports can't use interpolation (to make sure it's always possible to tell where mixins, functions, and variables come from), plain CSS imports can. This makes it possible to dynamically generate imports, for example based on mixin parameters.
{% codeExample 'interpolation' %} @mixin google-font($family) { @import url("http://fonts.googleapis.com/css?family=#{$family}"); }
@mixin google-font($family) @import url("http://fonts.googleapis.com/css?family=#{$family}")
@include google-font("Droid Sans") {% endcodeExample %}
{% render 'doc_snippets/module-system-status' %}
Sass's module system integrates seamlessly with @import, whether you're
importing a file that contains @use rules or loading a file that contains
imports as a module. We want to make the transition from @import to @use as
smooth as possible.
When you import a file that contains @use rules, the importing file has access
to all members (even private members) defined directly in that file, but not
any members from modules that file has loaded. However, if that file contains
@forward rules, the importing file will have access to forwarded members.
This means that you can import a library that was written to be used with the
module system.
{% headsUp %}
When a file with @use rules is imported, all the CSS transitively loaded by
those is included in the resulting stylesheet, even if it's already been
included by another import. If you're not careful, this can result in bloated
CSS output!
{% endheadsUp %}
An API that makes sense for @use might not make sense for @import. For
example, @use adds a namespace to all members by default so you can safely use
short names, but @import doesn't so you might need something longer. If you're
a library author, you may be concerned that if you update your library to use
the new module system, your existing @import-based users will break.
To make this easier, Sass also supports import-only files. If you name a file
<name>.import.scss, it will only be loaded for imports, not for @uses. This
way, you can retain compatibility for @import users while still providing a
nice API for users of the new module system.
{% codeExample 'import-only-files', false %} // _reset.scss
@include reset.list().
@mixin list() {
ul {
margin: 0;
padding: 0;
list-style: none;
}
}// _reset.import.scss
@include reset-list().
@forward "reset" as reset-*;// _reset.sass
@include reset.list().
@mixin list()
ul
margin: 0
padding: 0
list-style: none// _reset.import.sass
// Legacy import users can keep writing @include reset-list().
@forward "reset" as reset-*
{% endcodeExample %}
{% compatibility 'dart: "1.24.0"', 'libsass: false', 'ruby: false' %}{% endcompatibility %}
You can configure modules that are loaded through an @import by defining
global variables prior the @import that first loads that module.
{% codeExample 'configuring-modules' %} // _library.scss $color: blue !default;
$color: blue !default
a { color: green; } {% endcodeExample %}
{% headsUp %}
Modules are only loaded once, so if you change the configuration after you
@import a module for the first time (even indirectly), the change will be
ignored if you @import the module again.
{% endheadsUp %}
When you use @use (or @forward) load a module that uses @import, that
module will contain all the public members defined by the stylesheet you load
and everything that stylesheet transitively imports. In other words,
everything that's imported is treated as though it were written in one big
stylesheet.
This makes it easy to convert start using @use in a stylesheet even before all
the libraries you depend on have converted to the new module system. Be aware,
though, that if they do convert their APIs may well change!
@use{% render 'doc_snippets/use-import-differences' %}