title: Arrow not appear in navbar Bootstrap 4 menu and sub menu
body: <p>I trying to use navbar component from Twitter Bootstrap 4 with nested sub menu, but the arrow in the menu item that has sub menu is not appear at all, i do not no why.</p>
  
  <p>here the arrow appears:</p>
  
  <p><a href="https://i.stack.imgur.com/J6xI4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/J6xI4.jpg" alt="here arrow appear"></a></p>
  
  <p>but not appear in my side:</p>
  
  <p><a href="https://i.stack.imgur.com/bQbSA.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bQbSA.jpg" alt="enter image description here"></a>
  Here's the basic outline of my html code:</p>
  
  <pre><code>&lt;div class="container-fluid"&gt;
      &lt;nav class="navbar navbar-expand-lg navbar-dark bg-dark fixed-top"&gt;
  
              &lt;a class="navbar-brand" asp-controller="Home" asp-action="Index"&gt;Right Way&lt;/a&gt;
  
              &lt;button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation"&gt;
                  &lt;span class="navbar-toggler-icon"&gt;&lt;/span&gt;
              &lt;/button&gt;
  
              &lt;div class="collapse navbar-collapse" id="navbarSupportedContent"&gt;
                  &lt;ul class="navbar-nav m-auto justify-content-center"&gt;
                      &lt;li class="nav-item active"&gt;
                          &lt;a class="nav-link" asp-controller="Home" asp-action="Index"&gt;Home &lt;span class="sr-only"&gt;(current)&lt;/span&gt;&lt;/a&gt;
                      &lt;/li&gt;
  
                      &lt;li class="nav-item dropdown"&gt;
                          &lt;a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"&gt;
                              Dropdown
                          &lt;/a&gt;
                          &lt;ul class="dropdown-menu" id="sss" aria-labelledby="navbarDropdownMenuLink"&gt;
                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Action&lt;/a&gt;&lt;/li&gt;
                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Another action&lt;/a&gt;&lt;/li&gt;
                              &lt;li class="dropdown-submenu"&gt;
                                  &lt;a class="dropdown-item dropdown-toggle" href="#"&gt;Submenu&lt;/a&gt;
                                  &lt;ul class="dropdown-menu"&gt;
                                      &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Submenu&lt;/a&gt;&lt;/li&gt;
                                      &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Submenu0&lt;/a&gt;&lt;/li&gt;
                                      &lt;li class="dropdown-submenu"&gt;
                                          &lt;a class="dropdown-item dropdown-toggle" href="#"&gt;Submenu 1&lt;/a&gt;
                                          &lt;ul class="dropdown-menu"&gt;
                                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Subsubmenu1&lt;/a&gt;&lt;/li&gt;
                                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Subsubmenu1&lt;/a&gt;&lt;/li&gt;
                                          &lt;/ul&gt;
                                      &lt;/li&gt;
                                      &lt;li class="dropdown-submenu"&gt;
                                          &lt;a class="dropdown-item dropdown-toggle" href="#"&gt;Submenu 2&lt;/a&gt;
                                          &lt;ul class="dropdown-menu"&gt;
                                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Subsubmenu2&lt;/a&gt;&lt;/li&gt;
                                              &lt;li&gt;&lt;a class="dropdown-item" href="#"&gt;Subsubmenu2&lt;/a&gt;&lt;/li&gt;
                                          &lt;/ul&gt;
                                      &lt;/li&gt;
                                  &lt;/ul&gt;
                              &lt;/li&gt;
                          &lt;/ul&gt;
  
                      &lt;/li&gt;
                  &lt;/ul&gt;
  
              &lt;/div&gt;
      &lt;/nav&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>that is my CSS code:</p>
  
  <pre><code>.navbar-nav li:hover &gt; ul.dropdown-menu {
      display: block;
  }
  
  .dropdown-submenu {
      position: relative;
  }
  
  .dropdown-submenu &gt; .dropdown-menu {
      top: 0;
      left: 100%;
      margin-top: -6px;
  }
  
  /* rotate caret on hover */
  .dropdown-menu &gt; li &gt; a:hover:after {
      text-decoration: underline;
      transform: rotate(-90deg);
  }
  </code></pre>
  
  <p>I do not know what the wrong i tried all my best.</p>