三级下拉菜单小示例

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<link rel="stylesheet" href="css.css">
</head>
<body>

<nav>
<ul>
<li><a href="#">Home</a></li>
<li><a href="#">Tutorials</a>
<ul>
<li><a href="#">Photoshop</a></li>
<li><a href="#">Illustrator</a></li>
<li><a href="#">Web Design</a>
<ul>
<li><a href="#">HTML</a></li>
<li><a href="#"> CSS</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#">Articles</a>
<ul>
<li><a href="#">Web Design</a></li>
<li><a href="#">User Experience</a></li>
</ul>
</li>
<li><a href="#">Inspiration</a></li>
</ul>
</nav>
</body>
</html>

/*nav {
margin: 100px auto;
text-align: center;
}*/

nav ul ul {
display: none;
}

nav ul li:hover > ul {
display: block;
}


nav ul {
background: #efefef;
/*background: linear-gradient(top, #efefef 0%, #bbbbbb 100%);
background: -moz-linear-gradient(top, #efefef 0%, #bbbbbb 100%);
background: -webkit-linear-gradient(top, #efefef 0%,#bbbbbb 100%); */
box-shadow: 0px 0px 9px rgba(0,0,0,0.15);
padding: 0 20px;
border-radius: 10px;
list-style: none;
position: relative;
display: inline-table;
}
/*nav ul:after {
content: ""; clear: both; display: block;
}*/

nav ul li {
float: left;
}
nav ul li:hover {
background: #4b545f;
background: linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -moz-linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -webkit-linear-gradient(top, #4f5964 0%,#5f6975 40%);
}
nav ul li:hover a {
color: #fff;
}

nav ul li a {
display: block; padding: 25px 40px;
color: #757575; text-decoration: none;
}


nav ul ul {
background: #5f6975; border-radius: 0px; padding: 0;
position: absolute; top: 100%;
}
nav ul ul li {
float: none;
border-top: 1px solid #6b727c;
border-bottom: 1px solid #575f6a; position: relative;
}
nav ul ul li a {
padding: 15px 40px;
color: #fff;
}
nav ul ul li a:hover {
background: #4b545f;
}

nav ul ul ul {
position: absolute; left: 100%; top:0;

原文地址:https://www.cnblogs.com/jinjinjin/p/5675349.html