@mixin collapse---alter() {
}

@mixin collapse() {
  height: 0;
  overflow: hidden;
  transition: all 0.4s;
  &:not(.open) {
    padding-top: 0;
    padding-bottom: 0;
  }
  @include collapse---alter;
}

@mixin collapse--open---alter() {
}

@mixin collapse--open {
  height: auto;
  @include collapse--open---alter;
}