The menu bar is displayed, and the focus of a certain level of menu will expand the corresponding lower level menu;
Need to select the parent-child element of the menu, use the> child selector.
If you use the descendant selector, the next level, the next level...will be displayed when a certain level of menu gets the focus.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
li {
list-style: none;
}
li ul {
display: none;
}
li:hover>ul{
display: block;
}
</style>
</head>
<body>
<ul class="nav">
<li>
<span>一级菜单111</span>
<ul>
<li>
<span>二级菜单1222</span>
<ul>
<li>
<span>三级菜单333</span>
<ul>
<li>四级菜单</li>
<li>四级菜单</li>
</ul>
</li>
</ul>
</li>
<li>二级菜单2222</li>
</ul>
</li>
<li>
<span>一级菜单222</span>
<ul>
<li>二级菜单1222</li>
<li>二级菜单2222</li>
</ul>
</li>
</ul>
</body>
</html>