JSFiddle - React, Tailwind, and code Playground

HTML

<div class="overlay"> </div>

<a href="#" class="openMenu">Открыть меню</a>

CSS

.overlay {
    position: fixed;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0,0,0,.5);
    display: none;
    z-index: 10;
}

JavaScript

$(".openMenu").click(function () {
      $(".overlay").fadeToggle("slow");
});
$(".overlay").click(function () {
      $(this).fadeToggle("slow");
});