Horizontal header menu implemented with CSS3

<nav class="dropdownmenu">
  <ul>
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    <li><a href="http://www.jochaho.com/wordpress/about-pritesh-badge/">jb51</a></li>
    <li><a href="#">Articles on HTML5 & CSS3</a>
      <ul id="submenu">
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      </ul>
    </li>
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  </ul>
</nav>

.dropdownmenu ul, .dropdownmenu li {
	margin: 0;
	padding: 0;
}
.dropdownmenu ul {
	background: gray;
	list-style: none;
	width: 100%;
}
.dropdownmenu li {
	float: left;
	position: relative;
	width:auto;
}
.dropdownmenu a {
	background: #30A6E6;
	color: #FFFFFF;
	display: block;
	font: bold 12px/20px sans-serif;
	padding: 10px 25px;
	text-align: center;
	text-decoration: none;
	-webkit-transition: all .25s ease;
	-moz-transition: all .25s ease;
	-ms-transition: all .25s ease;
	-o-transition: all .25s ease;
	transition: all .25s ease;
}
.dropdownmenu li:hover a {
	background: #000000;
}
#submenu {
	left: 0;
	opacity: 0;
	position: absolute;
	top: 35px;
	visibility: hidden;
	z-index: 1;
}
li:hover ul#submenu {
	opacity: 1;
	top: 40px; /* adjust this as per top nav padding top & bottom comes */
	visibility: visible;
}
#submenu li {
	float: none;
	width: 100%;
}
#submenu a:hover {
	background: #DF4B05;
}
#submenu a {
	background-color:#000000;
}