最后一个HTML列表项上的圆角底角？

我的这些下拉菜单运行正常，但菜单的底角没有四舍五入。我包括了html，css和jquery代码。您知道为什么我的最后一个列表项没有显示圆角吗？

感谢您的时间！

的HTML

    <nav>
    <ul>
        <li><a id="Me" href="#">About Me</a>
        <li><a href="#">Favorite Films</a>
            <!-- Films Drop-Down Menu -->
            <ul>
                <li><a id="DC" href="#">DC Cinematic Universe</a></li>
                <li><a id="Bond" href="#">James Bond</a></li>
                <li><a id="Marvel" href="#">Marvel Cinematic Universe</a></li>
                <li><a id="ST" href="#">Star Trek</a></li>
                <li><a id="SW" href="#">Star Wars</a></li>
                <li><a id="X" href="#">X-Men</a></li>
            </ul>
            <!-- /Films Drop-Down Menu -->
        </li>
        <li><a href="#">Favorite TV Shows</a>
            <!-- TV Drop Down Menu -->
            <ul>
                <li><a id="Americans" href="#">Americans, The</a></li>
                <li><a id="GoT" href="#">Game of Thrones</a></li>
            </ul>
            <!-- /TV Drop Down Menu -->
        </li>
    </ul>
</nav>

的CSS

        nav {
    width: 100%;
    height: 2em;
    float: left;
    position: relative;
    background: linear-gradient(hsl(1,79%,30%), hsl(1, 88%, 44%), hsl(2,90%,26%));
    border: hsl(1,79%,30%) 2px solid;
    border-radius: 20px 20px 0 0;
}

nav ul {
    list-style: none;
}

nav li {
    width: 33%;
    display: inline;
    float: left;
    position: relative;
}

nav li a {
    /* Makes entire block for link clickable - not just text. */
    display: block;
    color: white;
    font-size: 1.5em;
    font-weight:bold;
    text-shadow: 5px 5px 5px black;
    transform:skewX(160deg);
    text-decoration: none;
}

nav li a:hover {
    color: #FFCC33;
}

nav ul ul {
    display: none;
    position: absolute;
    background: hsla(1,79%,30%,.8);
    /*Z-Index enables layering - higher values put elements toward top */
    z-index: 99;
}

nav li li {
    float: none;
    width: 100%;
    position: relative;
    padding: 10px;
    /*border: 1px hsl(1,79%,30%);*/
}

nav li li a {
    font-size: 1.25em;
}

/* Round bottom corners of menu items on bottom of drop-down menus.  */
nav li li:last-child {
    border-radius: 0 0 20px 20px;
}

JQUERY

    //DROP-DOWN MENUS
$('nav li').hover(function() {
    // stop() stops all animation before slideDown()
    $('ul',this).stop().slideDown(250);
},
    //When not hovering.
    function(){
        $('ul',this).stop().slideUp(250);
    }
);
//DROP-DOWN MENUS