JSFiddle - React, Tailwind, and code Playground

HTML

<div class="link_menu" id="foo">
        Menu software
  </div>
  <div class="menu" id="menu_left">
    <ul class="test">
      <li class ="test1">
        <a href="#">test1</a>
      </li>
      <li class ="test2">
        <a href="#">test2</a>
      </li>
    </ul>
   </div>

CSS

.link_menu {
    background-color: #CCCCCC;
    border-radius: 0 0 5px 5px;
    font-size: 14px;
    font-weight: bold;
    margin-left: 1px;
    padding-bottom: 5px;
    padding-top: 11px;
    text-align: center;
}

element.style {
    display: block;
}
#menu_left {
    display: none;
    margin-top: 30px;
}
.menu {
    margin-top: 0;
}
.menu {
    background: linear-gradient(to right, #FFFFFF, #FAFAFA) repeat scroll 0 0 rgba(0, 0, 0, 0);
    border-color: #D3D3D3;
    border-radius: 0 10px 10px 0;
    border-style: solid;
    border-width: 1px 1px 1px 0;
    margin-top: 42px;
    padding-left: 0;
    width: 80%;
}

ul.menu_partie {
    list-style-type: none;
    margin-bottom: 5px;
    margin-left: 0;
    margin-top: 5px;
    padding-left: 0;
    width: 160px;
}

JavaScript

function cachemontre(id) {
    x=document.getElementById(id);
    if(x.style.display==""){x.style.display="block"};
    if (x.style.display=="none") {x.style.display="block" ; }
    else {x.style.display="none" ;}
}

document.getElementById('foo').onclick= function(){
cachemontre('menu_left')}