JSFiddle - React, Tailwind, and code Playground

HTML

<nav id="main-nav">
    <ul id="main-menu">
        <li>	<a href="#">Atendimento</a>

            <ul>

                <li><a href="#">HelpDesk</a>

                </li>
                <li><a href="#">Chat</a>

                </li>
                <li><a href="#">E-mail</a>

                </li>
                <li><a href="#">Telefones</a>

                </li>

                <li><a href="#">Base de Conhecimento</a>

                </li>
                <li><a href="#">Nosso Blog</a>

                </li>
                <li><a href="#">Wiki</a>

                </li>
                <li class="vazio"></li>
            </ul>
        </li>
        <li>	<a href="#">Sobre nós</a>

            <ul>
                <li><a href="#">Serviços</a>

                </li>
                <li><a href="#">Sobre Nós</a>

                </li>
                <li><a href="#">Termos de Uso</a>

                </li>
                <li><a href="#">Política de Privacidade</a>

                </li>
                <li><a href="#">Testemunios</a>

                </li>
            </ul>
        </li>
        <li><a href="#login" data-toggle="modal" title="Acessar Painel de Controle"><i class="icon-signin"></i> Login</a>

        </li>
    </ul>
    <!--end:main-menu-->
</nav>
<!--end:main-nav-->

CSS

nav ul > li {
    overflow:hidden;
    margin-top:0;
    height:100%;
}

nav ul ul {
    margin-top: -120%;
    z-index: -1;
    -webkit-transition: margin 1s ease-in;
    -moz-transition: margin 1s ease-in;
    -o-transition: margin 1s ease-in;
    -ms-transition: margin 1s ease-in;
    transition: margin 1s ease-in;
}
nav ul li:hover > ul {
    margin-top: 0;
}
nav ul {
    background: #efefef;
    background: linear-gradient(top, #efefef 0%, #bbbbbb 100%);
    background: -moz-linear-gradient(top, #efefef 0%, #bbbbbb 100%);
    background: -webkit-linear-gradient(top, #efefef 0%, #bbbbbb 100%);
    box-shadow: 0px 0px 9px rgba(0, 0, 0, 0.15);
    padding: 0 20px;
    border-radius: 10px;
    list-style: none;
    position: relative;
    display: inline-table;
}
nav ul:after {
    content:"";
    clear: both;
    display: block;
}
nav ul li {
    float: left;
}
nav ul li:hover {
    background: #4b545f;
    background: linear-gradient(top, #4f5964 0%, #5f6975 40%);
    background: -moz-linear-gradient(top, #4f5964 0%, #5f6975 40%);
    background: -webkit-linear-gradient(top, #4f5964 0%, #5f6975 40%);
}
nav ul li:hover a {
    color: #fff;
}
nav ul li a {
    display: block;
    padding: 25px 40px;
    color: #757575;
    text-decoration: none;
}
nav ul ul {
    background: #5f6975;
    border-radius: 0px;
    padding: 0;
    position: absolute;
    top: 100%;
}
nav ul ul li {
    float: none;
    border-top: 1px solid #6b727c;
    border-bottom: 1px solid #575f6a;
    position: relative;
}
nav ul ul li a {
    padding: 15px 40px;
    color: #fff;
}
nav ul ul li a:hover {
    background: #4b545f;
}