onmouseover/onmouseout

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Events</title>
</head>
<body>
    <div id="text">some text</div>
</body>
<script>
   let element = document.getElementById('text');

   element.onmouseover = function () {
       this.style.border = '3px solid green';
   }

   element.onmouseout = function () {
       this.style.border = '';
   }
</script>
</html>