In addition to variables and nesting, Sass has multiple constructs that reduce repetition.

In Sass, a mixin lets you make groups of CSS declarations that you want to reuse throughout your site.

The notation for creating a mixin is as follows:

@mixin backface-visibility {
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  -moz-backface-visibility: hidden;
  -ms-backface-visibility: hidden;
  -o-backface-visibility: hidden;
}

Note: Mixin names and all other Sass identifiers use hyphens and underscores interchangeably. The following code:

.notecard {
.front, .back {
    width: 100%;
    height: 100%;
    position: absolute;

    @include backface_visibility;
  }
}

is equivalent to the following CSS:

.notecard .front, .notecard .back {
  width: 100%;
  height: 100%;
  position: absolute;

   backface-visibility: hidden;
  -webkit-backface-visibility: hidden; 
  -moz-backface-visibility: hidden;
  -ms-backface-visibility: hidden;
  -o-backface-visibility: hidden;
}