Bootstrap/site/assets/scss/_sidebar.scss

.bd-links {
  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;
  }

  a {
    padding: .1875rem .5rem;
    margin-top: .125rem;
    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);
    }

    // Indent if there's no submenu
    &:only-child {
      margin-left: 1.25rem;
    }

    // Add chevron if there's a submenu
    &:not(:only-child) {
      &::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%;
      }

      &:not(.collapsed) {
        color: rgba($black, .85);

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

    // Adjust font size and font weights in submenu
    + ul {
      @include font-size(.875rem);
    }
  }

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