JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" class="help" id="MyHelp" value="?" />
<div class ="content">
hjkh
</div>
<div id="helpwindow">
jkh
</div>

CSS

.help { background-color: blue;
        color: white;
        border-radius: 50%;
        position: fixed;
        right: 10px;
        }
.content{
  height: 800px;
}
#helpwindow{
  height: 800px;
  position: fixed;
  width: 150px;
  left: 0;
  top: 0;
  background-color: red;
  border: solid 1px grey;
  display: none;
}
.show{ display: block !important; }

JavaScript

//$(function(){
function ShowHelp() {
let element = document.getElementById("helpwindow");
  element.classList.toggle("show");
}
document.getElementById('MyHelp').addEventListener('click',ShowHelp);
//});