CSS 下拉菜单：z-index 问题

Question

我的 CSS 下拉菜单有两个问题：JSFiddle

1) Transitions: 当鼠标切换到打开菜单时，希望菜单向下滑动。之前打开的菜单应该向上滑动关闭。

#nav ul li ul
{
    -webkit-transition:height .5s ease-in;
    -moz-transition:height .5s ease-in;
    -o-transition:height .5s ease-in;
    -ms-transition:height .5s ease-in;
    transition:height .5s ease-in;
}

这似乎行不通；可能在错误的 "ul li" 选择器下，尽管我尝试了其他选择器。

2) 将父项 ("Menu1"、"Menu2") 置于菜单项列表的顶部，使其覆盖第一个子项的上边框。也就是说，"Menu1" 和 "Item1" 之间应该没有边框，因为 "Menu1" 没有底边框，但看起来像底边框，因为 "Item1" 在它上面.

尝试使用 z-index，但无法运行。转换都没有。

我发现菜单有点复杂，可能 CSS 超出了需要。

Answer 1

怎么样？ JSFiddle

#nav ul {
    padding: 0;
    margin: 0;
    list-style: none;
}

#nav ul li {
    display: inline-block;
    border: 1px solid #FFF;
    border-bottom: 0;
    border-radius: 5px;
    margin: 0 15px;
    position: relative;
    -webkit-transition: border-color 0.2s ease-in;
    -moz-transition: border-color 0.2s ease-in;
    -o-transition: border-color 0.2s ease-in;
    -ms-transition: border-color 0.2s ease-in;
    transition: border-color 0.2s ease-in;
}

#nav ul li a {
    color: #8799B3;
    display: block;
    padding: 10px 6px;
    border: 0;
    -webkit-transition: color 0.2s ease-in;
    -moz-transition: color 0.2s ease-in;
    -o-transition: color 0.2s ease-in;
    -ms-transition: color 0.2s ease-in;
    transition: color 0.2s ease-in;
}

#nav ul li:hover {
    color: #415161;
    border-color: #E9E9E9;
}

#nav ul li a:hover {
    color: #415161;
}

#nav ul li ul {
    opacity: 0;
    visibility: hidden;
    text-decoration: none;
    line-height: 1;
    color: #8799B3;
    background: #FFF;
    position: absolute;
    top: calc(100% - 5px);
    left: -1px;
    z-index: 1000;
    width: 165px;
    border: 0;
}

#nav ul li:hover ul {
    opacity: 1;
    visibility: visible;
}

#nav ul li ul li {
    border: 0;
    display: block;
    font-size: 14px;
    margin: 0;
    -webkit-transition: background 0.2s ease-in;
    -moz-transition: background 0.2s ease-in;
    -o-transition: background 0.2s ease-in;
    -ms-transition: background 0.2s ease-in;
    transition: background 0.2s ease-in;
}

#nav ul li ul li:hover {
    border: none;
    color: #415161;
    background: #F7F9FB;
}

#nav ul li ul li a {
    padding: 10px;
    border: none;
    color: #8799B3;
    border-left: 1px solid #E9E9E9;
    border-right: 1px solid #E9E9E9;
    border-bottom: 1px solid #E9E9E9;
}

#nav ul li ul li:first-child a {
    border-top: 1px solid #E9E9E9;
    border-radius: 0 5px 0 0;
}

#nav ul li ul li:last-child a {
    border-bottom: 1px solid #E9E9E9;
    border-radius: 0 0 5px 5px;
}

#nav ul li ul {
    -webkit-transition: opacity 0.2s ease-in;
    -moz-transition: opacity 0.2s ease-in;
    -o-transition: opacity 0.2s ease-in;
    -ms-transition: opacity 0.2s ease-in;
    transition: opacity 0.2s ease-in;
}

<div id="nav">
    <ul>
        <li>
            <a href="#">Menu1</a>
            <ul>
                <li><a href="menu.html">Item1</a></li>
                <li><a href="menu.html">Item2</a></li>
                <li><a href="menu.html">Item3</a></li>
                <li><a href="menu.html">Item4</a></li>
            </ul>
        </li>
        <li>
            <a href="#">Menu2</a>
            <ul>
                <li><a href="menu.html">Item1</a></li>
                <li><a href="menu.html">Item2</a></li>
                <li><a href="menu.html">Item3</a></li>
                <li><a href="menu.html">Item4</a></li>
            </ul>
        </li>
        <li>
            <a href="#">Menu3</a>
            <ul>
                <li><a href="menu.html">Item1</a></li>
                <li><a href="menu.html">Item2</a></li>
                <li><a href="menu.html">Item3</a></li>
                <li><a href="menu.html">Item4</a></li>
            </ul>
        </li>
    </ul>
</div>

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