html - 我无法将 置于 div 中

Question

我不能让ul在div元素中居中

        <div class="top-menu">
        <ul class="topnav dropdown" a>
            <li><a href="#">Home</a></li>
            <li>
                <a href="#">Tutorials</a>
                <ul class="subnav">
                    <li>
                    <a href="#">Sub Nav Link</a>
                        <ul class="subnav">
                            <li><a href="#">Sub Nav Link</a>
                                <ul class="subnav">
                                    <li><a href="#">Sub Nav Link</a></li>
                                    <li><a href="#">Sub Nav Link</a></li>
                                </ul> 
                            </li>
                            <li><a href="#">Sub Nav Link</a></li>
                        </ul>            
                    </li>
                    <li><a href="#">Sub Nav Link</a></li>
                </ul>
            </li>
            <li>
                <a href="#">Resources</a>
                <ul class="subnav">
                    <li><a href="#">Sub Nav Link</a></li>
                    <li><a href="#">Sub Nav Link</a></li>
                </ul>
            </li>
            <li><a href="#">About Us</a></li>
            <li><a href="#">Advertise</a></li>
            <li><a href="#">Submit</a></li>
            <li><a href="#">Contact Us</a></li>
        </ul>
    </div>

和CSS样式

.top-menu{
    width:100%;
    text-align:center;

}
ul.topnav {
    border:1px solid black;
    list-style: none;
    padding: 0 20px;    
    margin: auto;
    width: 100%;
    background: #222;
    background: url(topnav_bg.gif) repeat-x;
}
ul.topnav li {
    float: left;
    margin: 0;  
    padding: 0 15px 0 0;
    position: relative; /*--Declare X and Y axis base for sub navigation--*/
    display: inline; 
}

怎么了？ fiddle 在这里 http://jsfiddle.net/m82LK/2/ , 谢谢

Answer 1

看到这个 FIDDLE

CSS:

.top-menu {
    width:100%;
    text-align:center;
}
ul.topnav {
    border:1px solid black;
    list-style: none;
    padding: 0 20px;
    margin: auto;
    width: 100%;
    background: #222;
    background: url(topnav_bg.gif) repeat-x;
}
ul.topnav li {
    display:inline-block;
    margin: 0;
    padding: 0 15px 0 0;
    position: relative;
    /*--Declare X and Y axis base for sub navigation--*/
}
ul.topnav li a {
    padding: 10px 5px;
    color: #aaaaaa;
    display: block;
    text-decoration: none;
}
ul.topnav li a:hover {
    background: url(topnav_hover.gif) no-repeat center top;
}
ul.topnav li span {
    /*--Drop down trigger styles--*/
    width: 17px;
    height: 35px;
    float: left;
    background: url(subnav_btn.gif) no-repeat center top;
}
ul.topnav li span.subhover {
    background-position: center bottom;
    cursor: pointer;
}
/*--Hover effect for trigger--*/
 ul.topnav li ul.subnav {
    list-style: none;
    position: absolute;
    /*--Important - Keeps subnav from affecting main navigation flow--*/
    left: 0;
    top: 35px;
    background: #333;
    margin: 0;
    padding: 0;
    display: none;
    float: left;
    width: 170px;
    border: 1px solid #111;
}
ul.topnav li ul.subnav li {
    margin: 0;
    padding: 0;
    border-top: 1px solid #252525;
    /*--Create bevel effect--*/
    border-bottom: 1px solid #444;
    /*--Create bevel effect--*/
    clear: both;
    width: 170px;
}
html ul.topnav li ul.subnav li a {
    float: left;
    width: 145px;
    background: #333 url(dropdown_linkbg.gif) no-repeat 10px center;
    padding-left: 20px;
}
html ul.topnav li ul.subnav li a:hover {
    /*--Hover effect for subnav links--*/
    background: #222 url(dropdown_linkbg.gif) no-repeat 10px center;
}