<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css"crossorigin="anonymous">

<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"  crossorigin="anonymous"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js" crossorigin="anonymous"></script>

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js" crossorigin="anonymous"></script>

​

<nav class="navbar navbar-expand-lg navbar-light bg-light">

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

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

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

  </button>

​

  <div class="navbar-collapse collapse show" id="navbarSupportedContent" style="">

    <ul class="navbar-nav mr-auto">

      <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>

      <li class="nav-item dropdown">

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

          Dropdown

        </a>

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

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

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

          <div class="dropdown-divider"></div>

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

        </div>

      </li>

<li class="nav-item dropdown">

        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown2" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">

          Dropdown

        </a>

        <div class="dropdown-menu" aria-labelledby="navbarDropdown2">

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

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

          <div class="dropdown-divider"></div>

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

        </div>

      </li>

      <li class="nav-item">

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

      </li>

    </ul>

    <form class="form-inline my-2 my-lg-0">

      <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">

      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>

    </form>

  </div>

</nav>