如何将浮动项目的无序列表居中于页面

<ul>
    <li><a href=\"index.html\">Home</a></li>
    <li><a href=\"index.html\">About</a></li>
    <li><a href=\"index.html\">Service</a></li>
    <li><a href=\"index.html\">Blog</a></li>
</ul>

ul {
    margin: 0px;
    padding: 0px;
    list-style: none;
}
ul li {
    float: left;
    line-height: 50px;
    margin-left: 5px;
    margin-right: 5px;
}
ul li a {
    display: block;
    height: 46px;
    padding-left: 5px;
    padding-right: 5px;
}

text-align: center