实现下拉
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style type="text/css">
ul{
list-style-type: none;
}
.a{
display: none;
}
.b:hover~ .a{
display:inline;
}
</style>
<title></title>
</head>
<body>
<ul>
<li class="b">手机品牌</li>
<li class="a">华为</li><br/>
<li class="a">小米</li><br/>
<li class="a">苹果</li><br/>
</ul>
</body>
</html>