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125 lines
4.8 KiB
Markdown
125 lines
4.8 KiB
Markdown
---
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title: Structure of a Stylesheet
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table_of_contents: true
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introduction: >
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Just like CSS, most Sass stylesheets are mainly made up of style rules that
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contain property declarations. But Sass stylesheets have many more features
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that can exist alongside these.
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complementary_content: |
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<nav aria-labelledby="page-sections" class="page-sections sl-c-list-navigation-wrapper sl-c-list-navigation-wrapper--collapsible">
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### Page Sections{#page-sections}
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- [Statements](#statements){.section}
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- [Overview](#statements)
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- [Universal Statements](#universal-statements)
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- [CSS Statements](#css-statements)
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- [Top-Level Statements](#top-level-statements)
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- [Other Statements](#other-statements)
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- [Expressions](#expressions){.section}
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- [Overview](#expressions)
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- [Literals](#literals)
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- [Operations](#operations)
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- [Other Expressions](#other-expressions)
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</nav>
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---
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## Statements
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A Sass stylesheet is made up of a series of _statements_, which are evaluated in
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order to build the resulting CSS. Some statements may have _blocks_, defined
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using `{` and `}`, which contain other statements. For example, a style rule is
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a statement with a block. That block contains other statements, such as property
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declarations.
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In SCSS, statements are separated by semicolons (which are optional if the
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statement uses a block). In the indented syntax, they're just separated by
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newlines.
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### Universal Statements
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These types of statements can be used anywhere in a Sass stylesheet:
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- [Variable declarations](../../variables), like `$var: value`.
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- [Flow control at-rules](../../at-rules/control), like `@if` and `@each`.
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- The [`@error`](../../at-rules/error), [`@warn`](../../at-rules/warn), and
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[`@debug`](../../at-rules/debug) rules.
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### CSS Statements
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These statements produce CSS. They can be used anywhere except within a
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`@function`:
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- [Style rules](../../style-rules), like `h1 { /* ... */ }`.
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- [CSS at-rules](../../at-rules/css), like `@media` and `@font-face`.
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- [Mixin uses](../../at-rules/mixin) using `@include`.
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- The [`@at-root` rule](../../at-rules/at-root).
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### Top-Level Statements
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These statements can only be used at the top level of a stylesheet, or nested
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within a CSS statement at the top level:
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- [Module loads](../../at-rules/use), using `@use`.
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- [Imports](../../at-rules/import), using `@import`.
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- [Mixin definitions](../../at-rules/mixin) using `@mixin`.
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- [Function definitions](../../at-rules/function) using `@function`.
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### Other Statements
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- [Property declarations](../../style-rules/declarations) like `width: 100px` may
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only be used within style rules and some CSS at-rules.
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- The [`@extend` rule](../../at-rules/extend) may only be used within style rules.
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## Expressions
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An _expression_ is anything that goes on the right-hand side of a property or
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variable declaration. Each expression produces a _[value][]_. Any valid CSS property
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value is also a Sass expression, but Sass expressions are much more powerful
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than plain CSS values. They're passed as arguments to [mixins][] and
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[functions][], used for control flow with the [`@if` rule][], and manipulated using
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[arithmetic][]. We call Sass's expression syntax _SassScript_.
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[value]: ../../values
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[mixins]: ../../at-rules/mixin
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[functions]: ../../at-rules/function
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[`@if` rule]: ../../at-rules/control/if
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[arithmetic]: ../../operators/numeric
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### Literals
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The simplest expressions just represent static values:
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- [Numbers](../../values/numbers), which may or may not have units, like `12` or
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`100px`.
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- [Strings](../../values/strings), which may or may not have quotes, like
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`"Helvetica Neue"` or `bold`.
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- [Colors](../../values/colors), which can be referred to by their hex
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representation or by name, like `#c6538c` or `blue`.
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- The [boolean](../../values/booleans) literals `true` or `false`.
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- The singleton [`null`](../../values/null).
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- [Lists of values](../../values/lists), which may be separated by spaces or commas
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and which may be enclosed in square brackets or no brackets at all, like
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`1.5em 1em 0 2em`, `Helvetica, Arial, sans-serif`, or `[col1-start]`.
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- [Maps](../../values/maps) that associate values with keys, like
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`("background": red, "foreground": pink)`.
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### Operations
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Sass defines syntax for a number of operations:
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{% render 'documentation/snippets/operator-list', parens:true %}
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### Other Expressions
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- [Variables](../../variables), like `$var`.
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- [Function calls](../../at-rules/function), like `nth($list, 1)` or
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`var(--main-bg-color)`, which may call Sass core library functions or
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user-defined functions, or which may be compiled directly to CSS.
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- [Special functions](special-functions), like `calc(1px + 100%)` or
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`url(http://myapp.com/assets/logo.png)`, that have their own unique parsing
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rules.
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- [The parent selector](../../style-rules/parent-selector), `&`.
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- The value `!important`, which is parsed as an unquoted string.
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