导航3种下拉

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<style>
/*一、下拉菜单ol折叠*/
*{margin: 0;padding: 0px}
ul{
200px;
height: 50px;
outline: 1px solid black;
}
ul li{
50%;
height: 100%;
outline: 1px solid black;
text-align: center;
float: left;
line-height: 50px;
list-style: none;
background: green;
}
ul ol{
100%;
height: 0;
transition: all linear 0.5s;
overflow: hidden;
outline: 1px solid black;
}
ul ol li{
100%;
height: 50px;
text-align: left;
background: pink;
outline: 1px solid black;
}
ul ol li a{
color: black;
text-decoration: none;
}
ul li:hover ol{
height: 150px;
transition: all linear 1s;
}
ul ol li:hover{
background: yellow;
}

</style>
</head>
<body>
<ul>
<li>帅哥
<ol>
<li><a href="#">罗晋</a></li>
<li><a href="#">刘志鹏</a></li>
<li><a href="#">周乐</a></li>
</ol>
</li>
<li>美女
<ol>
<li><a href="#">刘涛</a></li>
<li><a href="#">范冰冰</a></li>
<li><a href="#">刘诗诗</a></li>
</ol>
</li>
</ul>
</body>
</html>

第二种

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<style>
/*二、下拉菜单li折叠*/
*{margin: 0;padding: 0px}
ul{
200px;
height: 50px;
outline: 1px solid black;
}
ul li{
50%;
height: 100%;
outline: 1px solid black;
text-align: center;
float: left;
line-height: 50px;
list-style: none;
background: green;
}
ul ol li{
100%;
/*变化*/
height: 0;
text-align: left;
background: pink;
outline: 1px solid black;
transition: all linear 1s;
overflow:hidden;
}
ul ol li a{
color: black;
text-decoration: none;
}
ul li:hover ol li{
height: 50px; /*变化*/
transition: all linear 1s;
}
ul ol li:hover{
background: yellow;
}
</style>
</head>
<body>
<ul>
<li>帅哥
<ol>
<li><a href="#">罗晋</a></li>
<li><a href="#">刘志鹏</a></li>
<li><a href="#">周乐</a></li>
</ol>
</li>
<li>美女
<ol>
<li><a href="#">刘涛</a></li>
<li><a href="#">范冰冰</a></li>
<li><a href="#">刘诗诗</a></li>
</ol>
</li>
</ul>
</body>
</html>

第三种

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<style>
/*三、挂面式二级菜单*/
*{margin: 0;padding: 0px}
ul{
200px;
height: 50px;
outline: 1px solid black;
}
ul li{
50%;
height: 100%;
outline: 1px solid black;
text-align: center;
float: left;
line-height: 50px;
list-style: none;
background: green;
}
ul ol{
100%;
height: 150px;
overflow: hidden;
outline: 1px solid black;
display: none;
}
ul ol li{
100%;
height: 50px;
text-align: left;
background: pink;
outline: 1px solid black;
}
ul ol li a{
color: black;
text-decoration: none;
}
ul li:hover ol{
display: block;
}
ul ol li:hover{
background: yellow;
}