JSFiddle - React, Tailwind, and code Playground

HTML

<div class="leftmenu block">
  <div class="lalala">

  </div>
</div>
<div class="leftmenu block">
  <div class="lalala">

  </div>
</div>
<div class="leftmenu block">
  <div class="lalala">

  </div>
</div>

CSS

.leftmenu.block{
margin-top:15px;
width:100px;
height:100px;
background:green;
display:block;
position: relative;
}
.leftmenu.block.open-block-leftmenu .lalala {
    position: absolute;
    top: 50px;
    left: 100%;
    width: 100px;
    height: 100px;
    background: red;
}

JavaScript

$(".leftmenu.block").click(function(){
		if ($(this).hasClass("open-block-leftmenu"))
		{
			$(this).removeClass("open-block-leftmenu");
		}
		else
		{
			$(".leftmenu.block").removeClass("open-block-leftmenu");
			$(this).addClass("open-block-leftmenu");
		}
	});