<!DOCTYPE html>
<html>
<head>
<script src="https://code.jquery.com/jquery-2.1.1.min.js"></script>
<meta charset="utf-8">
<title>JS Bin</title>
<style>
* {
margin: 0;
padding: 0;
border: 0;
}
body {
font-size: 25px;
color: #fff;
font-family: 'Microsoft Sans Serif';
}
#header {
height: 1000px;
background-color: gray;
}
#nav {
height: 40px;
background-color: red;
text-align: center;
}
#text {
background-color: #CCC;
height: 2000px;
}
.sticky {
position: fixed;
width: 100%;
top: 0;
}
</style>
</head>
<body>
<div id="wrapper">
<header>
<div id="header">
</div>
</header>
<nav>
<div id="nav">
<div id="logo_nav"></div>
<div id="tel_nav"><p>Телефон</p></div>
</div>
</nav>
<div id="text">
</div>
</div>
<script>
var nav = $("#nav"),
header = $('header').height();
$(window).scroll(function() {
if( $(this).scrollTop() > header ) {
nav.addClass('sticky');
} else {
nav.removeClass('sticky');
}
});
</script>
</body>
</html>