@mixin arrow($direction: down, $size: 5px, $color: #555) {

  width: 0;
  height: 0;
  @if ($direction == left) {
    border-top: $size solid transparent;
    border-bottom: $size solid transparent;
    border-right: $size solid $color;
  }
  @else if ($direction == right) {
    border-top: $size solid transparent;
    border-bottom: $size solid transparent;
    border-left: $size solid $color;
  }
  @else if ($direction == down) {
    border-left: $size solid transparent;
    border-right: $size solid transparent;
    border-top: $size solid $color;
  }
  @else {
    border-left: $size solid transparent;
    border-right: $size solid transparent;
    border-bottom: $size solid $color;
  }
}