---
title: Structure of a Stylesheet
table_of_contents: true
introduction: >
  Just like CSS, most Sass stylesheets are mainly made up of style rules that
  contain property declarations. But Sass stylesheets have many more features
  that can exist alongside these.
---

## Statements

A Sass stylesheet is made up of a series of _statements_, which are evaluated in
order to build the resulting CSS. Some statements may have _blocks_, defined
using `{` and `}`, which contain other statements. For example, a style rule is
a statement with a block. That block contains other statements, such as property
declarations.

In SCSS, statements are separated by semicolons (which are optional if the
statement uses a block). In the indented syntax, they're just separated by
newlines.

### Universal Statements

These types of statements can be used anywhere in a Sass stylesheet:

- [Variable declarations](/documentation/variables), like `$var: value`.
- [Flow control at-rules](/documentation/at-rules/control), like `@if` and
  `@each`.
- The [`@error`](/documentation/at-rules/error),
  [`@warn`](/documentation/at-rules/warn), and
  [`@debug`](/documentation/at-rules/debug) rules.

### CSS Statements

These statements produce CSS. They can be used anywhere except within a
`@function`:

- [Style rules](/documentation/style-rules), like `h1 { /* ... */ }`.
- [CSS at-rules](/documentation/at-rules/css), like `@media` and `@font-face`.
- [Mixin uses](/documentation/at-rules/mixin) using `@include`.
- The [`@at-root` rule](/documentation/at-rules/at-root).

### Top-Level Statements

These statements can only be used at the top level of a stylesheet, or nested
within a CSS statement at the top level:

- [Module loads](/documentation/at-rules/use), using `@use`.
- [Imports](/documentation/at-rules/import), using `@import`.
- [Mixin definitions](/documentation/at-rules/mixin) using `@mixin`.
- [Function definitions](/documentation/at-rules/function) using `@function`.

### Other Statements

- [Property declarations](/documentation/style-rules/declarations) like `width:
100px` may only be used within style rules and some CSS at-rules.
- The [`@extend` rule](/documentation/at-rules/extend) may only be used within
  style rules.

## Expressions

An _expression_ is anything that goes on the right-hand side of a property or
variable declaration. Each expression produces a _[value][]_. Any valid CSS
property value is also a Sass expression, but Sass expressions are much more
powerful than plain CSS values. They're passed as arguments to [mixins][] and
[functions][], used for control flow with the [`@if` rule][], and manipulated
using [arithmetic][]. We call Sass's expression syntax _SassScript_.

[value]: /documentation/values
[mixins]: /documentation/at-rules/mixin
[functions]: /documentation/at-rules/function
[`@if` rule]: /documentation/at-rules/control/if
[arithmetic]: /documentation/operators/numeric

### Literals

The simplest expressions just represent static values:

- [Numbers](/documentation/values/numbers), which may or may not have units,
  like `12` or `100px`.
- [Strings](/documentation/values/strings), which may or may not have quotes,
  like `"Helvetica Neue"` or `bold`.
- [Colors](/documentation/values/colors), which can be referred to by their hex
  representation or by name, like `#c6538c` or `blue`.
- The [boolean](/documentation/values/booleans) literals `true` or `false`.
- The singleton [`null`](/documentation/values/null).
- [Lists of values](/documentation/values/lists), which may be separated by
  spaces or commas and which may be enclosed in square brackets or no brackets
  at all, like `1.5em 1em 0 2em`, `Helvetica, Arial, sans-serif`, or
  `[col1-start]`.
- [Maps](/documentation/values/maps) that associate values with keys, like
  `("background": red, "foreground": pink)`.

### Operations

Sass defines syntax for a number of operations:

{% render 'doc_snippets/operator-list', parens: true %}

### Other Expressions

- [Variables](/documentation/variables), like `$var`.
- [Function calls](/documentation/at-rules/function), like `nth($list, 1)` or
  `var(--main-bg-color)`, which may call Sass core library functions or
  user-defined functions, or which may be compiled directly to CSS.
- [Special functions](/documentation/syntax/special-functions), like
  `calc(1px + 100%)` or `url(http://myapp.com/assets/logo.png)`, that have their
  own unique parsing rules.
- [The parent selector](/documentation/style-rules/parent-selector), `&`.
- The value `!important`, which is parsed as an unquoted string.