btn btn-outline-info my-2 my-sm-0

  <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
    <a class="navbar-brand" href="#">ブランド</a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav"
      aria-controls="navbarNav" aria-expanded="false" aria-label="ナビゲーション切替">
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarNav">
      <ul class="navbar-nav mr-auto">
        <li class="nav-item"><a class="nav-link" href="#">リンク1</a></li>
        <li class="nav-item"><a class="nav-link" href="#">リンク2</a></li>
        <li class="nav-item"><a class="nav-link" href="#">リンク3</a></li>
      </ul>
      <!-- アウトラインの検索ボタン、darkだど映える -->
      <form class="form-inline my-2 my-lg-0">
        <input class="form-control mr-sm-2" type="search" placeholder="検索" aria-label="検索">
        <button class="btn btn-outline-info my-2 my-sm-0" type="submit">検索</button>
      </form>
    </div>
  </nav>