下面的这个应该怎么做啊？，。
为什么我做的下拉菜单里的爱好那里会不显示二级菜单呢？求大家解答！
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
ul,li {
list-style-type: none;
margin: 0;
padding: 0;
}
.menu .menu-item {
float: left;
cursor: pointer;
padding: 0 10px;
width: auto;
height: 30px;
line-height: 30px;
border: 1px solid #999;
border-right: none;
position: relative;
}
.menu .menu-item:after {
clear: both;
}
.menu .menu-item:last-child {
border-right: 1px solid #999;
}
.sub-menu {
display: none;
position: absolute;
width: 100%;
top: 30px;
left: -1px;
}
.sub-menu li {
float: left;
text-align: center;
font-size: 14px;
width: 100%;
height: 20px;
line-height: 20px;
border: 1px solid #999;
}
.sub-menu li:hover {
color: blue;
}
.menu .menu-item .sub-menu:hover,
.menu .menu-item:hover .sub-menu {
display: block;
}
</style>
</head>
<body>
<ul class="menu">
<li class="menu-item">
<span>A菜单</span>
<ul class="sub-menu">
<li>A1菜单</li>
<li>A2菜单</li>
</ul>
</li>
<li class="menu-item">
<span>B菜单</span>
<ul class="sub-menu">
<li>B1菜单</li>
<li>B2菜单</li>
</ul>
</li>
</ul>
</body>
</html>
把你的代码发下看看
这种百度搜索一大堆，各种样式都可以
```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.menu_box{
width: 300px;
}
.ul_box{
display: flex;
}
.li_item{
position: relative;
width: 100px;
}
li{
list-style: none;
text-align: center;;
}
.a{
position: absolute;
width: 150px;
left: -85%;
display: none;
}
.li_item:hover .a{
display: block;
}
</style>
</head>
<body>
<div class="menu_box">
<ul class="ul_box">
<li class="li_item">
<span>aaa</span>
<ul class="a">
<li>二级菜单</li>
<li>二级菜单</li>
<li>二级菜单</li>
</ul>
</li>
<li class="li_item">
<span>bbb</span>
<ul class="a">
<li>1级菜单</li>
<li>1级菜单</li>
<li>1级菜单</li>
</ul>
</li>
<li class="li_item">ccc</li>
</ul>
</div>
</body>
</html>
```
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>利用css制作二级下拉菜单</title>
<style type="text/css">
* {
margin: 0;
padding: 0;/* 清除内外边距 */
}
div {
margin: 0px auto;/* 盒子给宽高之后,margin: 0px auto;居中才会生效 */
width: 300px;
height: 300px;
background-color: pink;
}
ul li {
list-style: none;/* 去掉元素前的小圆点 */
}
ul a {
text-decoration: none;/* 去掉字体的下划线 */
}
ul li {/* 一级菜单的样式 */
float: left;
width: 100px;
height: 36px;
line-height: 36px;/* 行高等于高使文字垂直居中 */
text-align: center;
background: #bcecdd;
}
ul li ul li {
display: none;/* 隐藏二级菜单 */
}
ul li:hover ul li { /* 鼠标经过时显示二级菜单 */
display: block;/* 二级菜单转化为块级元素,使其独占一行 */
}
ul li:hover {
background-color: springgreen;/* 鼠标经过时显示的背景颜色 */
}
</style>
</head>
<body>
<div>
<ul>
<li><a href="">一级</a>
<ul>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
</ul>
</li>
<li><a href="">一级</a>
<ul>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
</ul>
</li>
<li><a href="">一级</a>
<ul>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
<li><a href="">二级</a></li>
</ul>
</li>
</ul>
</div>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
.dropdown {
position: relative;
display: inline-block;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
padding: 12px 16px;
}
.dropdown:hover .dropdown-content {
display: block;
}
</style>
</head>
<body>
<h2>鼠标移动后出现下拉菜单</h2>
<p>将鼠标移动到指定元素上就能看到下拉菜单。</p>
<div class="dropdown">
<span>一级菜单</span>
<div class="dropdown-content">
<p>二级菜单1</p>
<p>二级菜单2</p>
</div>
</div>
</body>
</html>