使用 position: fixed; 固定顶部，菜单下拉栏就无法用；
测试网页：https://www.hxw.ltd/cdl.html
取消position: fixed;，菜单下拉栏就可以使用，菜单栏就无法固定在顶部。
测试网页：https://www.hxw.ltd/cdl-1.html
position: fixed;
求解？？？？
下方为完整代码页
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>顶部菜单栏</title>
<style>
body {margin:0;}
ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: #333;
position: fixed;
top: 0;
width: 100%;
}
li {
float: left;
border-right:1px solid #bbb;
}
li:last-child {
border-right: none;
}
li a {
display: block;
color: white;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}
li a:hover:not(.active) {
background-color: #111;
}
.active {
background-color: #4CAF50;
}
li a, .dropbtn {
display: inline-block;
color: white;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}
li a:hover, .dropdown:hover, .dropbtn {
background-color: #111;
}
.dropdown {
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);
}
.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
}
.dropdown-content a:hover {background-color: #f1f1f1}
.dropdown:hover .dropdown-content {
display: block;
}
</style>
</head>
<body>
<ul>
<li><a class="active" href="#home">主页</a></li>
<li><a href="#news">新闻</a></li>
<li><a href="#contact">联系</a></li>
<li><a href="#about">关于</a></li>
<li>
<div class="dropdown">
<a href="#" class="dropbtn">下拉菜单1</a>
<div class="dropdown-content">
<a href="#">链接 1</a>
<a href="#">链接 2</a>
<a href="#">链接 3</a>
</div>
</div>
</li>
<li>
<div class="dropdown">
<a href="#" class="dropbtn">下拉菜单2</a>
<div class="dropdown-content">
<a href="#">链接 1</a>
<a href="#">链接 2</a>
<a href="#">链接 3</a>
</div>
</div>
</li>
</ul>
<div style="padding:20px;margin-top:30px;height:1500px;">
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
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<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
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<p>Some text some text some text some text..</p>
<p>Some text some text some text some text..</p>
</div>
</body>
</html>
