<===> input.scss
@mixin sprite-arrow() {
  @extend %hidden-text;
}

%hidden-text {
  text-indent: -999em;
}

// button.scss
.button-left,
.button-right,
.button-plus,
.button-min {
  &:after {
      @include sprite-arrow();
  }
}

.banner {
  &:after {
      @include sprite-arrow();
  }
}

.calculator {
  .btn-down,
  .btn-up {
      &:after {
          @include sprite-arrow();
      }
  }
}
<===> output.css
.calculator .btn-down:after,
.calculator .btn-up:after, .banner:after, .button-left:after,
.button-right:after,
.button-plus:after,
.button-min:after {
  text-indent: -999em;
}