.#{$content-holder} {
  margin-left: auto;
  margin-right: auto;
  width: $content-max-width + $layout-unit;
  max-width: calc(100% - 2 * #{$content-min-margin + $layout-unit});
}

.#{$center-vertically} {
  @include display-flex;
  height: 100%;
  &.#{horizontally} {
    justify-content: center;
  }
  > * {
    align-self: center;
  }
}