container py-5 d-flex justify-content-center

  <div class="container py-5 d-flex justify-content-center">
    <!-- 左方向へのドロップ -->
    <div class="btn-group dropleft">
      <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true"
        aria-expanded="false">左方向へのドロップ</button>
      <div class="dropdown-menu" aria-labelledby="dropdownMenuLink">
        <a class="dropdown-item" href="#">メニュー01</a>
        <a class="dropdown-item" href="#">メニュー02</a>
        <a class="dropdown-item" href="#">メニュー03</a>
      </div>
    </div>
  </div>

  <div class="container py-5 d-flex justify-content-center">
    <!-- 右方向へのドロップ -->
    <div class="btn-group dropright">
      <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true"
        aria-expanded="false">右方向へのドロップ</button>
      <div class="dropdown-menu" aria-labelledby="dropdownMenuLink">
        <a class="dropdown-item" href="#">メニュー01</a>
        <a class="dropdown-item" href="#">メニュー02</a>
        <a class="dropdown-item" href="#">メニュー03</a>
      </div>
    </div>
  </div>

  <div class="container py-5 d-flex justify-content-center">
    <!-- 上方向へのドロップ -->
    <div class="btn-group dropup">
      <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true"
        aria-expanded="false">上方向へのドロップ</button>
      <div class="dropdown-menu" aria-labelledby="dropdownMenuLink">
        <a class="dropdown-item" href="#">メニュー01</a>
        <a class="dropdown-item" href="#">メニュー02</a>
        <a class="dropdown-item" href="#">メニュー03</a>
      </div>
    </div>
  </div>