sass-site/source/documentation/at-rules/index.md

title	introduction
At-Rules	Much of Sass’s extra functionality comes in the form of new [at-rules](https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule) it adds on top of CSS:

• @use loads mixins, functions, and variables from other Sass stylesheets, and combines CSS from multiple stylesheets together.

• @forward loads a Sass stylesheet and makes its mixins, functions, and variables available when your stylesheet is loaded with the @use rule.

• @import extends the CSS at-rule to load styles, mixins, functions, and variables from other stylesheets.

• @mixin and @include makes it easy to re-use chunks of styles.

• @function defines custom functions that can be used in SassScript expressions.

• @extend allows selectors to inherit styles from one another.

• @at-root puts styles within it at the root of the CSS document.

• @error causes compilation to fail with an error message.

• @warn prints a warning without stopping compilation entirely.

• @debug prints a message for debugging purposes.

• Flow control rules like @if, @each, @for, and @while control whether or how many times styles are emitted.

Sass also has some special behavior for plain CSS at-rules: they can contain interpolation, and they can be nested in style rules. Some of them, like @media and @supports, also allow SassScript to be used directly in the rule itself without interpolation.