papercss/src/components/_accordion.scss

.collapsible {
  display: flex;
  flex-direction: column;

  &:nth-of-type(1) {
    border-top: 1px solid $muted-light;
  }

  .collapsible-body {
    @include transition;
    background-color: lighten($white-dark, 80%);
    border-bottom: 1px solid $muted-light;
    margin: 0;
    max-height: 0;
    opacity: 0;
    overflow: hidden;
    padding: 0 0.75rem;
  }

  input {
    display: none;

    &:checked + label {
      color: $primary;
    }

    &[id^='collapsible']:checked~div.collapsible-body {
      margin: 0;
      max-height: 960px;
      opacity: 1;
      padding: 0.75rem;
    }
  }

  label {
    border-bottom: 1px solid $muted-light;
    color: $primary;
    display: inline-block;
    font-weight: 600;
    margin: 0 0 -1px;
    padding: 0.75rem;
    text-align: center;

    &:hover {
      color: $muted;
      cursor: pointer;
    }
  }
}