Onmouseover Event

<!DOCTYPE html>
<html lang=en>
<head>
<title></title>
<meta charset=utf-8>
<meta name="viewport" content="width=device-width">
<style>
a { font-size:15px;font-family:arial;font-weight:900;color:white;
    text-decoration:none;display:block;margin:50px 5px; }
.bar {  width:250px;height:100vh;transition: all 0.2s linear;                          background-color:red;display:inline-block;position:fixed;
        top:0;margin:0;left:-250px;  }
.text { font-size:50px;text-align:center;margin:40px 0;display:block; }
.H { font-size:90px;text-align:center;margin:40px 0;font-family:arial;  }
.F { font-size:90px;text-align:center;margin:40px 0 90px 0;
     font-family:arial;  }
h2 {  margin:50px 0;padding:0 20px 0 50px;text-indent:100px;
      font-size:25px;line-height:50px; }
#close_nav {  float:right;  }
#open_bar {  position:fixed;top:10px;  }

</style>
</head>
<body>

<div class='container'>
<button onclick='open_bar()' id='open_bar'>Navigation Bar</button>
<span id='bar' onmouseleave='enable()' onmouseover='disable()' class='bar'>
<button onclick='shut()' id='close_nav'>close</button>
<a target='_blank' href='https://www.w3schools.com/jsref/event_onmouseover.asp'>Onmouseover Event</a>
</span>
<h1 class='H'>Header</h1>
<span class='text'>Some text</span>
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</div>
<h1 class='F'>Footer</h1>


<script>
window.onbeforeunload = function () {
  window.scrollTo(0, 0);
}

function shut(){
bar.style.left = '-250px';
}

function open_bar(){
bar.style.left = '0';
}
function disable(){
document.body.style.overflow='hidden';
}
function enable(){
document.body.style.overflowY='scroll';
}

</script>
</body>
</html>