JSFiddle - React, Tailwind, and code Playground

HTML

<nav>
  <ul class="menu">
    <li><a href="#">Home</a></li><!--
    --><li><a href="#">Accueil</a>
      <ul class="sous-menu">
        <li><a href="#">Conseils</a></li>
        <li><a href="#">Produits</a></li>
        <li><a href="#">Activités</a></li>
      </ul>
    </li><!--
    --><li><a href="#">Contact</a>
      <ul class="sous-menu">
        <li><a href="#">By Mail</a></li>
        <li><a href="#">By Phone</a></li>
      </ul>
    </li>
  </ul>
</nav>

CSS

*{
  box-sizing: border-box;
  padding:0;
  margin: 0;
}

nav{
  background-color: #808080;
  border-radius: 5px;
}

.menu::after{
  content: '';
  display: block;
  clear: both;
}

ul{
  list-style-type: none;
}

.menu > li > a{
  color: white;
  border-radius: 5px;
  display: block;  
  font-size: 1em;
  padding: 10px 30px;
  text-decoration: none;
}

.menu{
  text-align: center;
  margin: 0 auto;
}

.menu > li{
  display: inline-block;
  position: relative;
}

.menu > li > a:hover{
  background-color:#595959;
}

.sous-menu{
  background-color: #D9D9D9;
  display: none;
  position: absolute;
  top: 39px;
  left: 0;
  width: 100%;
}

.sous-menu > li > a{
  color: white;
  border-radius: 5px;
  display: block;  
  font-size: 1em;
  padding: 10px 20px;
  text-decoration: none;
}

.sous-menu > li > a:hover{
  background-color: black;
}

.menu > li:hover .sous-menu{
  display: block;
}