.bd-subnavbar {
  background-color: rgba($white, .75);
  backdrop-filter: blur(1rem);
  box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .05), inset 0 -1px 0 rgba(0, 0, 0, .15);

  .dropdown-menu {
    @include font-size(.875rem);
    box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .05);
  }

  .dropdown-item.active {
    font-weight: 600;
    color: $gray-900;
    background: escape-svg($dropdown-active-icon) no-repeat .4rem .6rem/.75rem .75rem;
  }

  @include media-breakpoint-up(md) {
    @supports (position: sticky) {
      position: sticky;
      top: 0;
      z-index: $zindex-sticky;
    }
  }
}

.bd-search {
  position: relative; // To contain the Algolia search

  @include media-breakpoint-down(sm) {
    width: 100%;
  }

  .form-control:focus {
    border-color: $bd-purple-bright;
    box-shadow: 0 0 0 3px rgba($bd-purple-bright, .25);
  }
}

.bd-search-docs-toggle {
  line-height: 1;
  color: $gray-900;
}

.bd-subnavbar {
  // The position and z-index are needed for the dropdown to stay on top of the content
  position: relative;
  z-index: $zindex-sticky;
  background-color: rgba($white, .75);
  backdrop-filter: blur(1rem);
  box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .05), inset 0 -1px 0 rgba(0, 0, 0, .15);

  .dropdown-menu {
    @include font-size(.875rem);
    box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .05);
  }

  .dropdown-item.active {
    font-weight: 600;
    color: $gray-900;
    background: escape-svg($dropdown-active-icon) no-repeat .4rem .6rem/.75rem .75rem;
  }

  @include media-breakpoint-up(md) {
    position: sticky;
    top: 0;
  }
}

.bd-search {
  position: relative; // To contain the Algolia search

  @include media-breakpoint-down(sm) {
    width: 100%;
  }

  .form-control:focus {
    border-color: $bd-purple-bright;
    box-shadow: 0 0 0 3px rgba($bd-purple-bright, .25);
  }
}

.bd-search-docs-toggle {
  line-height: 1;
  color: $gray-900;
}

Make sure the content doesn't cover the navbar dropdown
Make sure the content doesn't cover the navbar dropdown

See https://github.com/twbs/bootstrap/pull/29368#issuecomment-528725686
