@each $horizontal in left right {
  .slide-position--#{$horizontal} {
    background-position: $horizontal;
  }

  @each $vertical in top bottom {
    .slide-position--#{$horizontal}-#{$vertical} {
      background-position: #{$horizontal} #{$vertical};
    }
  }
}

@each $position in top bottom center {
  .slide-position--#{$position} {
    background-position: $position;
  }
}