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, like $var: value.
• Flow control at-rules, like @if and @each.
• The @error, @warn, and @debug rules.

CSS Statements

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

• Style rules, like h1 { /* ... */ }.
• CSS at-rules, like @media and @font-face.
• Mixin uses using @include.
• The @at-root rule.

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, using @use.
• Imports, using @import.
• Mixin definitions using @mixin.
• Function definitions using @function.

Other Statements

• Property declarations like width: 100px may only be used within style rules and some CSS at-rules.
• The @extend rule 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.

Literals

The simplest expressions just represent static values:

• Numbers, which may or may not have units, like 12 or 100px.
• Strings, which may or may not have quotes, like "Helvetica Neue" or bold.
• Colors, which can be referred to by their hex representation or by name, like #c6538c or blue.
• The boolean literals true or false.
• The singleton null.
• Lists of values, 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 that associate values with keys, like ("background": red, "foreground": pink).

Operations

Sass defines syntax for a number of operations:

• == and != are used to check if two values are the same.
• +, -, *, /, and % have their usual mathematical meaning for numbers, with special behaviors for units that matches the use of units in scientific math.
• <, <=, >, and >= check whether two numbers are greater or less than one another.
• and, or, and not have the usual boolean behavior. Sass considers every value “true” except for false and null.
• +, -, and / can be used to concatenate strings.
• ( and ) can be used to explicitly control the precedence order of operations.

Other Expressions

• Variables, like $var.
• Function calls, like nth($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, like calc(1px + 100%) or url(http://myapp.com/assets/logo.png), that have their own unique parsing rules.
• The parent selector, &.
• The value !important, which is parsed as an unquoted string.