zdoc/assets/sass/components/_menu.scss

.menu {
  position: -webkit-sticky;
  position: sticky;
  top: $grid-nav-height;
  padding: 0.5rem;
  margin: 0.5rem;
  margin-top: 0;
  padding-top: 0.85rem;
  height: calc(100vh - $grid-nav-height);
  overflow-y: auto;
  z-index: z('menu');

  &__label {
    font-family: $title-font;
    font-size: 1rem;
    margin: 0.65rem 0;
    padding-bottom: 0.5rem;
    text-transform: capitalize;

    @include themify($themes) {
      color: themed('toc-label-color');
    }

    @media only screen and (max-width: 600px) {
      text-align: center;
      font-size: 1.125rem;
    }
  }

  &__title {
    cursor: pointer;
    position: relative;
    word-break: break-word;
    font-size: 0.925rem;
    height: $menu-title-height;
    margin: 0.25rem 0;

    @include no-select;
    @include flexbox();
    @include align-items(center);
    @include themify($themes) {
      color: themed('body-color');
      
      @include on-event {
        color: themed('no-active-font-color');
      }

      &.active {
        font-weight: bold;
        color: themed('active-font-color');
      }
    }

    &--collapse {
      cursor: pointer;
      word-break: break-word;
      font-size: 16px;
      height: $menu-title-height;
      margin: 0.25rem 0;

      @include no-select;
      @include flexbox();
      @include align-items(center);
      @include themify($themes) {
        color: themed('body-color');

        &.active {
          font-weight: bold;
          color: themed('active-font-color');

          svg {
            color: themed('active-font-color');
          }
        }
      }

      @include on-event {
        @include themify($themes) {
          color: themed('link-hover');
          svg {
            color: themed('link-hover');
            @include translateX(0.125rem);
          }
        }
      }
    }

    &--icon {
      margin-top: 2px;

      @include themify($themes) {
        color: themed('menu-arrow-color');
      }

      &.down {
        @include rotate(90);
        @include transition(all, 0.15s, ease);
      }

      &.right {
        @include rotate(0);
        @include transition(all, 0.15s, ease);
      }

      svg {
        display: block;
        margin: auto 0;
        @include transition(all, 0.15s, ease);
      }
    }
  }

  &__alone {
    cursor: pointer;
    @include no-select;
  }

  &__list {
    max-height: 0;
    overflow: hidden;
    word-wrap: break-word;
    
    @include transition();

    .active {
      font-weight: bold;
    }

    li {
      margin-left: 1.25rem;

      &.active {
        font-weight: bold;
      }
    }
  }

  .active {
    max-height: 100%;
  }

  li.active {
    @include themify($themes) {
      a {
        font-weight: bold;
      }
    }
  }
}