hacks-guide-minimal-mistakes-theme/docs/_sass/minimal-mistakes/_mixins.scss

/* ==========================================================================
   MIXINS
   ========================================================================== */

%tab-focus {
  /* Default*/
  outline: thin dotted $warning-color;
  /* Webkit*/
  outline: 5px auto $warning-color;
  outline-offset: -2px;
}

/*
   em function
   ========================================================================== */

@function em($target, $context: $doc-font-size) {
  @return ($target / $context) * 1em;
}


/*
   Bourbon clearfix
   ========================================================================== */

/*
  * Provides an easy way to include a clearfix for containing floats.
  * link http://cssmojo.com/latest_new_clearfix_so_far/
  *
  * example scss - Usage
  *
  * .element {
  *   @include clearfix;
  * }
  *
  * example css - CSS Output
  *
  * .element::after {
  *   clear: both;
  *   content: "";
  *   display: table;
  * }
*/

@mixin clearfix {
  clear: both;

  &::after {
    clear: both;
    content: "";
    display: table;
  }
}