JSFiddle - React, Tailwind, and code Playground

HTML

<button class="btn-mobile">btn</button>
<div class="menuMobile">
    11111111 1111111
</div>

CSS

.menuMobile{  
  background: #ccc;
  padding: 10px;
  position: absolute;
  visibility: hidden;
  opacity: 0;
  transition: 0.6s;
  transform: translate(0, -100%);  
}
.menuMobile.current{
  visibility: visible;
  opacity: 1;
  transform: translate(0, 100%); 
}

JavaScript

var btnMenuMobile = document.getElementsByClassName("btn-mobile")[0];
var menuMobile = document.getElementsByClassName("menuMobile")[0];


btnMenuMobile.addEventListener("click", function(){
  menuMobile.classList.toggle("current");
}, false);