CodePen

HTML

            
              <link href='http://fonts.googleapis.com/css?family=PT+Sans:400,700' rel='stylesheet' type='text/css'>
	<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
	<script>
		$(function() {
			var pull 		= $('#pull');
				menu 		= $('nav ul');
				menuHeight	= menu.height();

			$(pull).on('click', function(e) {
				e.preventDefault();
				menu.slideToggle();
			});

			$(window).resize(function(){
        		var w = $(window).width();
        		if(w > 320 && menu.is(':hidden')) {
        			menu.removeAttr('style');
        		}
    		});
		});
	</script>
</head>
<body>
	<nav class="clearfix">
		<ul class="clearfix">
            
			<li><a href="#">Home</a></li>
			<li><a href="#">How-to</a></li>
			<li><a href="#">Icons</a></li>
			<li><a href="#">Design</a></li>
			<li><a href="#">Web 2.0</a></li>
			<li><a href="#">Tools</a>
      <!--submenu-->
     <ul class="submenu">
       <li>
         <a href="#">Option1</a>
         <a href="#">Option2</a>
       </li>
       
       
        </ul>
      <!--submenu ends-->
      </li>	
		</ul>
		<a href="#" id="pull">Menu</a>
	</nav>
</body>
            
          
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CSS

            
              .clearfix:before,
.clearfix:after {
    content: " ";
    display: table;
}
.clearfix:after {
    clear: both;
}
.clearfix {
    *zoom: 1;
}

nav {
	height: 40px;
	width: 100%;
	background: #455868;
	font-size: 11pt;
	font-family: 'PT Sans', Arial, sans-serif;
	font-weight: bold;
	position: relative;
	border-bottom: 2px solid #283744;
}
nav ul {
	padding: 0;
	margin: 0 auto;
	width: 600px;
	height: 40px;
}
nav li {
	display: inline;
	float: left;
  position:relative;
}

nav li:hover{
  display:block; float:left;
   background-color: #ff0000;  
}

nav li:hover .submenu {left:0;	
}

.submenu{display:block; position:absolute; z-index:100;
  top:auto; left:999em;
}

nav li ul{
	padding: 0;
	margin: 0 0;
	width: 100px;
	height: auto;
}

nav li ul li{
  background: #455868;
	display: block;
	float: none;
}

nav li ul li a{
  background: #455868;
	color: #fff;
  display: inline-block;
	width: 100px;
	text-align: center;
	text-decoration: none;
	line-height: 40px;
	text-shadow: 1px 1px 0px #283744;
  border-right: none;
	box-sizing:border-box;
	-moz-box-sizing:border-box;
	-webkit-box-sizing:border-box;
  border-bottom: 1px solid #576979;
}



nav a {
	color: #fff;
	display: inline-block;
	width: 100px;
	text-align: center;
	text-decoration: none;
	line-height: 40px;
	text-shadow: 1px 1px 0px #283744;
}
nav li a {
	border-right: 1px solid #576979;
	box-sizing:border-box;
	-moz-box-sizing:border-box;
	-webkit-box-sizing:border-box;
}
nav li:last-child a {
	border-right: 0;
}
nav a:hover, nav a:active {
	background-color: #8c99a4;
}
nav a#pull {
	display: none;
}

/*Styles for screen 600px and lower*/
@media screen and (max-width: 600px) {
	nav { 
  		height: auto;
  	}
  	nav ul {
  		width: 100%;
  		display: block;
  		height: auto;
  	}
  	nav li {
  		width: 50%;
  		float: left;
  		position: relative;
  	}
  	nav li a {
		border-bottom: 1px solid #576979;
		border-right: 1px solid #576979;
	}
  	nav a {
	  	text-align: left;
	  	width: 100%;
	  	text-indent: 25px;
  	}
}

/*Styles for screen 515px and lower*/
@media only screen and (max-width : 480px) {
	nav {
		border-bottom: 0;
	}
	nav ul {
		display: none;
		height: auto;
	}
	nav a#pull {
		display: block;
		background-color: #283744;
		width: 100%;
		position: relative;
	}
	nav a#pull:after {
		content:"";
		background: url('nav-icon.png') no-repeat;
		width: 30px;
		height: 30px;
		display: inline-block;
		position: absolute;
		right: 15px;
		top: 10px;
	}
}

/*Smartphone*/
@media only screen and (max-width : 320px) {
	nav li {
		display: block;
		float: none;
		width: 100%;
	}
	nav li a {
		border-bottom: 1px solid #576979;
	}
}

ul li ul.submenu{display:none;}
ul li:hover ul.submenu{ display:block}
            
          
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