Sass mixin to justifiy navbar links in Bootstrap 4, see also http://bassjobsen.weblogs.fm/bootstrap-4s-responsive-navbars/

gistfile1.txt

// Justified nav links
// -------------------------

@mixin nav-justified($breakpoint: md) {
  width: 100%;

  .nav-item {
    float: none;
  }

  .nav-link {
    text-align: center;
    margin-bottom: 5px;
  }

  > .dropdown .dropdown-menu { //todo: remove child selector
    top: auto;
    left: auto;
  }

  @include media-breakpoint-up($breakpoint) {
    .nav-item {
      display: table-cell;
      width: 1%;
    }
    .nav-link {
        margin-bottom: 0;
    }
  }
}