keiji/html/css/bootstrap-5.0.2/site/assets/scss/_sidebar.scss

.bd-sidebar {
  @include media-breakpoint-down(md) {
    margin: 0 -.75rem 1rem;
  }
}

.bd-links {
  overflow: auto;
  font-weight: 600;

  @include media-breakpoint-up(md) {
    position: sticky;
    top: 5rem;
    // Override collapse behaviors
    // stylelint-disable-next-line declaration-no-important
    display: block !important;
    height: subtract(100vh, 7rem);
    // Prevent focus styles to be cut off:
    padding-left: .25rem;
    margin-left: -.25rem;
    overflow-y: auto;
  }

  > ul {
    @include media-breakpoint-down(md) {
      padding: 1.5rem .75rem;
      background-color: $gray-100;
      border-bottom: 1px solid $gray-200;
    }
  }

  a {
    padding: .1875rem .5rem;
    margin-top: .125rem;
    margin-left: 1.25rem;
    color: rgba($black, .65);
    text-decoration: if($link-decoration == none, null, none);

    &:hover,
    &:focus {
      color: rgba($black, .85);
      text-decoration: if($link-hover-decoration == underline, none, null);
      background-color: rgba($bd-purple-bright, .1);
    }
  }

  .btn {
    // Custom styles (as we don't have a completely neutral button style)
    padding: .25rem .5rem;
    font-weight: 600;
    color: rgba($black, .65);
    background-color: transparent;
    border: 0;

    &:hover,
    &:focus {
      color: rgba($black, .85);
      background-color: rgba($bd-purple-bright, .1);
    }

    &:focus {
      box-shadow: 0 0 0 1px rgba($bd-purple-bright, .7);
    }

    // Add chevron if there's a submenu
    &::before {
      width: 1.25em;
      line-height: 0; // Align in the middle
      content: escape-svg($sidebar-collapse-icon);
      @include transition(transform .35s ease);
      transform-origin: .5em 50%;
    }

    &[aria-expanded="true"] {
      color: rgba($black, .85);

      &::before {
        transform: rotate(90deg);
      }
    }
  }

  .active {
    font-weight: 600;
    color: rgba($black, .85);
  }
}