source/documentation/at-rules/index.md
@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.