JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block" id="categories_block_left">
    <div class="block_content">
        <ul class="tree dhtml">
                                    
<li>
    <a title="" href="/category.php?id_category=2">MER</a>
            <ul>
                                    
<li>
    <a title="" href="/category.php?id_category=5">SAUMON</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=6">POISSONS FUMES / SALES</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=7">ANCHOIS</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=8">THON</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=9">POISSONS FUMES / SALES / MARINES</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=10">CAVIAR, ŒUFS DE POISSON, OURSIN </a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=11">TERRINES &amp; TARTNABLES</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=12">CRUSTACES, MOLLUSQUES, CEPHALOPODES</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=13">SOUPES - BISQUES - VELOUTES</a>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=14">MAREE</a>
    </li>
                                                
<li class="last">
    <a title="" href="/category.php?id_category=17">JAPON EXTREME ORIENT</a>
    </li>
                            </ul>
    </li>
                                                
<li>
    <a title="" href="/category.php?id_category=3">TERROIR</a>
            <ul>
                                    
<li...

CSS

#categories_block_left {
z-index: 1;
}

#categories_block_left ul {
  background: none repeat scroll 0 0 #F0F0F0;
  float: left;
  z-index: 1;
}

#categories_block_left li {
border-bottom: 1px solid #FFFFFF;
float: left;
position: relative;
}

#categories_block_left ul ul  li {
border-bottom: 0;
 background: none repeat scroll 0 0 #F0F0F0;
 z-index: 9999;
}

#categories_block_left ul ul  li a {
 z-index: 9999;
 width: 172px;
}

#categories_block_left li a {
  color: #000000;
  display: block;
  font-family: "Droid Sans",arial,sans-serif;
  font-size: 12px;
  line-height: 3.333em;
  padding: 0 6px;
  text-decoration: none;
  text-transform: uppercase;
    
}





#categories_block_left ul ul {
    -moz-box-shadow: 0 3px 3px rgba(0,0,0,0.2);
    -webkit-box-shadow: 0 3px 3px rgba(0,0,0,0.2);
    box-shadow: 0 3px 3px rgba(0,0,0,0.2);
    display: none;
    float: left;
    margin: 0;
    position: absolute;
    top: 35px;
    left: 0;
    width: 188px;
    z-index: 9999;
}


#categories_block_left ul ul ul {
    left: 100%;
    top: 0;
    z-index: 9999;
}
#categories_block_left ul ul a {
    background: #f9f9f9;
    border-bottom: 1px dotted #ddd;
    color: #444;
    font-size: 12px;
    font-weight: normal;
    height: auto;
    line-height: 1.4em;
    padding: 10px 10px;
    width: 223px;
    z-index: 9999;
}
#categories_block_left li:hover > a,
#categories_block_left ul ul :hover > a,
#categories_block_left a:focus {
    background: #92B5B9;
}
#categories_block_left li:hover > a,
#categories_block_left a:focus {
    background: #92B5B9; 
    color: #fff;
}
#categories_block_left ul li:hover ul {
    display: block;
    z-index: 9999;
}
#categories_block_left .current-menu-item > a,
#categories_block_left .current-menu-ancestor > a,
#categories_block_left .current_page_item > a,
#categories_block_left .current_page_ancestor > a {
    font-weight: bold;
}