JSFiddle - React, Tailwind, and code Playground

HTML

<div class="cont">
START
</div>
<div class="box">Move the mouse cursor inside this box and observe the mouseenter event fires (background goes green). Next, use the mouse wheel to scroll down without moving the mouse cursor position, observe the mouseleave event doesn't fire. Finally, move the mouse cursor even a little, say 1px, and observe that the mouseleave event then fires</div>

<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
END
</div>
PASTEND

CSS

.box {
    font-family: arial;
    font-size: 16px;
    width: 300px;
    height: 200px;
    background-color: #000077;
    color: #ffffff;
}
.cont {
  height: 200px;
  overflow: auto;
}

JavaScript

var box = document.getElementsByClassName('box')[0];

box.addEventListener('mouseenter', function (e) {
	document.body.setAttribute('style', 'background-color: #007700');
});

box.addEventListener('mouseleave', function (e) {
	document.body.setAttribute('style', 'background-color: #ffffff');
});