Bootstrap class: .navbar-expand-*

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo02" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <a class="navbar-brand" href="#">Navbar</a>

  <div class="collapse navbar-collapse" id="navbarTogglerDemo02">
    <ul class="navbar-nav mr-auto mt-2 mt-md-0">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Link</a>
      </li>
    </ul>
  </div>
</nav>

Preview

Sass source

/* _navbar.scss:140 */
.navbar-expand {
  @each $breakpoint in map-keys($grid-breakpoints) {
    $next: breakpoint-next($breakpoint, $grid-breakpoints);
    $infix: breakpoint-infix($next, $grid-breakpoints);

    &#{$infix} {
      @include media-breakpoint-down($breakpoint) {
        > .container,
        > .container-fluid {
          padding-right: 0;
          padding-left: 0;
        }
      }

      @include media-breakpoint-up($next) {
        flex-flow: row nowrap;
        justify-content: flex-start;

        .navbar-nav {
          flex-direction: row;

          .dropdown-menu {
            position: absolute;
          }

          .nav-link {
            padding-right: $navbar-nav-link-padding-x;
            padding-left: $navbar-nav-link-padding-x;
          }
        }

        // For nesting containers, have to redeclare for alignment purposes
        > .container,
        > .container-fluid {
          flex-wrap: nowrap;
        }

        .navbar-collapse {
          display: flex !important;  // stylelint-disable-line declaration-no-important

          // Changes flex-bases to auto because of an IE10 bug
          flex-basis: auto;
        }

        .navbar-toggler {
          display: none;
        }
      }
    }
  }
}

Uses variables

Code copied to the clipboard.

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/* _navbar.scss:140 */
$breakpoint
$grid-breakpoints
$next:
$breakpoint
$grid-breakpoints
$infix:
$next
$grid-breakpoints
$infix}
$breakpoint
$next
$navbar-nav-link-padding-x
$navbar-nav-link-padding-x

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