First of all, clear your float. EDIT: One of my friend has got real problems with div inside , so lets change this.
<div class="header-box">
<nav>
<ul>
<li>AASD</li>
<li>AASD</li>
<li>AASD</li>
<li style="visibility:hidden;opacity:0;height:0;width:0;clear:both"></li>
</ul>
</nav>
</div>
and the styles:
<style>
.header-box {
width: 400px;
height: 49px;
border: 1px solid green;
position: relative;
}
ul {
margin: 0 auto;
padding: 0;
text-align: center;
height: 100%;
margin: 13px auto;
}
nav li {
float: none;
list-style-type: none;
/* padding-left: 19px; */
/* margin-left: 20px; */
/* line-height: 50px; */
display: inline-block;
/* top: 0px; */
margin: 0 auto;
text-align: center;
}
</style>