JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<link rel="stylesheet" href="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css">
<div id="main-nav" class="justify-content-end">
  <ul id="menu-main-menu" class="navbar-nav">
    <li class="menu-item current-menu-item current_page_item menu-item-home active nav-item"><a href="#" class="nav-link">Main Menu 1</a>
    </li>
    <li class="menu-item menu-item-has-children dropdown nav-item"><a href="#" data-toggle="dropdown" class="dropdown-toggle nav-link">Main Menu 2</a>
      <ul class="dropdown-menu" role="menu">
        <li class="menu-item menu-item-has-children dropdown nav-item"><a href="#" class="dropdown-item">Menu 1</a>
          <ul class="dropdown-menu" role="menu">
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 1</a></li>
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 2</a></li>
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 3</a></li>
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 4</a></li>
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 5</a></li>
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 6</a></li>
          </ul>
        </li>
        <li class="menu-item menu-item-has-children dropdown nav-item"><a href="#" class="dropdown-item">Menu 2</a>
          <ul class="dropdown-menu" role="menu">
            <li class="menu-item nav-item"><a href="#" class="dropdown-item">Sub Menu 11</a></li>
            <li class="menu-item nav-item"><a href="#"...

CSS

.navbar-nav {
    -ms-flex-direction: row;
    flex-direction: row;
}
.navbar-nav .dropdown-menu {
    position: absolute;
}
.navbar-nav > li:last-child {
   float: right;
}
.navbar-nav > li {
  margin: 0 15px;
}
.dropdown-menu .dropdown-toggle::after {
  border-bottom: 0.3em solid transparent;
  border-left: 0.3em solid;
  border-top: 0.3em solid transparent;
}
.dropdown-menu.show {
  border: 1px solid #999;
  background-color: #ffffff;
}
.dropdown.menu-item-has-children .dropdown.menu-item-has-children {
    position: unset;
}
.dropdown.menu-item-has-children .dropdown.menu-item-has-children>.dropdown-menu {
    top: 0;
    left: 100%;
    margin-top: -6px;
    margin-left: -1px;
    -webkit-border-radius: 4px;
    -moz-border-radius: 4px;
    border-radius: 4px;
    box-shadow: 0 1px 6px 0 rgba(0, 0, 0, 0.11);
    background-color: #ffffff;
    border: 1px solid #999;
}
.dropdown.menu-item-has-children .dropdown.menu-item-has-children:hover>.dropdown-menu {
    display: block;
}

.dropdown.menu-item-has-children .dropdown.menu-item-has-children>a:after {
    display: block;
    content: " ";
    float: right;
    width: 0;
    height: 0;
    border-color: transparent;
    border-style: solid;
    border-width: 5px 0 5px 5px;
    border-left-color: #ccc;
    margin-top: 5px;
    margin-right: -10px;
}

.dropdown.menu-item-has-children .dropdown.menu-item-has-children:hover>a:after {
    border-left-color: #fff;
}

.dropdown.menu-item-has-children .dropdown.menu-item-has-children.pull-left {
    float: none;
}

.dropdown.menu-item-has-children .dropdown.menu-item-has-children.pull-left>.dropdown-menu {
    left: -100%;
    margin-left: 10px;
    -webkit-border-radius: 6px 0 6px 6px;
    -moz-border-radius: 6px 0 6px 6px;
    border-radius: 6px 0 6px 6px;
}