Vertically center with inline-block and a dummy element

_mixins.scss

// Vertically center with inline-block and a dummy element
// @mixin   vertically-center-child
// @see     http://css-tricks.com/centering-in-the-unknown/
@mixin vertically-center-child(
  $child-selector: "&:first-child",
  $font-size: $base-font-size,
  $collapse-white-space: if($font-size, true, false),
  $dummy-selector: "&:before"
) {
  @if $collapse-white-space {
    font-size: 0;
  }

  #{$child-selector} {
    @include inline-block;
    @if $font-size {
      font-size: $font-size;
    }
  }
  #{$dummy-selector} {
    @include inline-block;
    content: "";
    height: 100%;
  }
}