bootstrap/docs/assets/scss/_sidebar.scss

// scss-lint:disable VendorPrefix

//
// Side navigation
//

.bd-toc {
  position: sticky;
  top: 4rem;
  max-height: calc(100vh - 4rem);
  padding-top: 1.5rem;
  padding-bottom: 1.5rem;
  overflow-y: auto;
  font-size: .85rem;
}

.section-nav {
  padding-left: 0;
  border-left: 1px solid #eee;

  ul {
    padding-left: 1rem;

    ul {
      display: none;
    }
  }
}

.toc-entry {
  display: block;

  a {
    display: block;
    padding: .25rem 1.5rem;
    color: #99979c;

    &:hover {
      color: $brand-primary;
      text-decoration: none;
    }
  }
}

.bd-sidebar {
  background-color: #f5f5f5;
  border-right: 1px solid rgba(0,0,0,.1);

  @include media-breakpoint-up(md) {
    position: sticky;
    top: 4rem;
    max-height: calc(100vh - 4rem);
    overflow-y: auto;
  }

  @include media-breakpoint-up(xl) {
    max-width: 320px;
  }
}

.bd-links {
  margin-right: -15px;
  margin-left: -15px;
}

.bd-search {
  position: relative;
  padding-top: 1rem;
  padding-bottom: 1rem;
}

.bd-search-results {
  right: 0;
  display: block;
  padding: 0;
  overflow: hidden;
  font-size: .85rem;

  &:empty {
    display: none;
  }

  .dropdown-item {
    padding-right: .75rem;
    padding-left: .75rem;

    &:first-child { margin-top: .25rem; }
    &:last-child { margin-bottom: .25rem; }
  }

  .no-results {
    padding: .75rem 1rem;
    color: #7a7a7a;
    text-align: center;
    white-space: normal; // Undo .dropdown-item defaults
  }
}


.bd-sidenav {
  display: none;
}

.bd-toc-link {
  display: block;
  padding: .75rem 1.5rem;
  font-weight: 500;
  color: $gray;
}

.bd-toc-link:hover {
  color: $brand-primary;
  text-decoration: none;
  background-color: #fafafa;
}

.bd-toc-item {
  &:first-child {
    border-top: 1px solid $gray-lighter;
  }
  &:not(:last-child) {
    border-bottom: 1px solid $gray-lighter;
  }

  &.active {
    background-color: #fafafa;

    > .bd-toc-link {
      color: $gray-dark;
    }

    > .bd-sidenav {
      display: block;
      padding-bottom: .75rem;
    }
  }
}

// All levels of nav
.bd-sidebar .nav > li > a {
  display: block;
  padding: .25rem 1.5rem;
  font-size: 90%;
  color: #99979c;
}

.bd-sidebar .nav > li > a:hover {
  color: $brand-primary;
  text-decoration: none;
  background-color: transparent;
}

.bd-sidebar .nav > .active > a,
.bd-sidebar .nav > .active:hover > a {
  font-weight: 500;
  color: $gray-dark;
  background-color: transparent;
}