foundation-sites/scss/prototype/_shadow.scss

// Foundation for Sites by ZURB
// foundation.zurb.com
// Licensed under MIT Open Source

////
/// @group prototype-shadow
////

/// Responsive breakpoints for shadow utility.
/// @type Boolean
$prototype-shadow-breakpoints: $global-prototype-breakpoints !default;

/// Default value for `prototype-box-shadow`
/// @type Number
$prototype-box-shadow: 0 2px 5px 0 rgba(0,0,0,.16),
                       0 2px 10px 0 rgba(0,0,0,.12) !default;

/// Shadow Utility: Adds a light box shadow to an element by default.
/// @param {Number} $shadow [$prototype-box-shadow] Box Shadow of a component
@mixin shadow(
  $shadow: $prototype-box-shadow
) {
  box-shadow: $shadow;
}

@mixin foundation-prototype-shadow {
  .shadow {
    @include shadow;
  }

  @if ($prototype-shadow-breakpoints) {
    // Loop through Responsive Breakpoints
    @each $size in $breakpoint-classes {
      @include breakpoint($size) {
        @if $size != $-zf-zero-breakpoint {
          .#{$size}-shadow {
            @include shadow;
          }
        }
      }
    }
  }
}