twbs--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: .875rem;
}

.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: #f5f2f9;
  border-bottom: 1px solid rgba(0,0,0,.1);

  @include media-breakpoint-up(md) {
    position: sticky;
    top: 4rem;
    max-height: calc(100vh - 4rem);
    overflow-y: auto;
    border-right: 1px solid rgba(0,0,0,.1);
  }

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

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

  // Override collapse behaviors
  @include media-breakpoint-up(md) {
    display: block !important;
  }
}

.bd-search {
  position: relative; // To contain the Algolia search
  padding-top: 1rem;
  padding-bottom: 1rem;
}

.bd-search-docs-toggle {
  line-height: 1;
  color: $gray-dark;
}

.bd-sidenav {
  display: none;
}

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

  &:hover {
    color: $brand-primary;
    text-decoration: none;
    background-color: rgba(0,0,0,.01);
  }
}

.bd-toc-item {
  border-bottom: 1px solid rgba(0,0,0,.05);

  &:first-child {
    border-top: 1px solid rgba(0,0,0,.05);
  }

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

      &:hover {
        background-color: transparent;
      }
    }

    > .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: rgba(0,0,0,.65);
}

.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;
}