Bootstrap/site/docs/4.3/assets/scss/_nav.scss

//
// Main navbar
//

.bd-navbar {
  min-height: 4rem;
  background-color: $bd-purple;
  box-shadow: 0 .5rem 1rem rgba(0, 0, 0, .05), inset 0 -1px 0 rgba(0, 0, 0, .1);

  @include media-breakpoint-down(md) {
    padding-right: .5rem;
    padding-left: .5rem;

    .navbar-nav-scroll {
      max-width: 100%;
      height: 2.5rem;
      margin-top: .25rem;
      overflow: hidden;

      .navbar-nav {
        padding-bottom: 2rem;
        overflow-x: auto;
        white-space: nowrap;
        -webkit-overflow-scrolling: touch;
      }
    }
  }

  @include media-breakpoint-up(md) {
    @supports (position: sticky) {
      position: sticky;
      top: 0;
      z-index: 1071; // over everything in bootstrap
    }
  }

  .navbar-nav {
    .nav-link {
      padding-right: .5rem;
      padding-left: .5rem;
      color: $bd-purple-light;

      &.active,
      &:hover {
        color: $white;
        background-color: transparent;
      }

      &.active {
        font-weight: 600;
      }
    }
  }

  .navbar-nav-svg {
    display: inline-block;
    width: 1rem;
    height: 1rem;
    vertical-align: text-top;
  }

  .dropdown-menu {
    @include font-size(.875rem);
  }

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