<a class="navbar-brand" href="#">Navbar</a>

  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">

    <span class="navbar-toggler-icon"></span>

  </button>

  <div class="collapse navbar-collapse" id="navbarNavDropdown">

    <ul class="navbar-nav">

      <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="#">Features</a>

      </li>

      <li class="nav-item">

        <a class="nav-link" href="#">Pricing</a>

      </li>

      <li class="nav-item dropdown">

        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">

          Dropdown link

        </a>

        <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">

          <a class="dropdown-item" href="#">Action</a>

          <a class="dropdown-item" href="#">Another action</a>

          <a class="dropdown-item" href="#">Something else here</a>

        </div>

      </li>

    </ul>

  </div>