创建下拉菜单：
<style>
*{
margin: 0px;
padding: 0px;
list-style: none;
}
#nav-banner{
border-radius: 10px; /*所有边框*/
500px;
height: 50px;
background-color: aqua;
}
.nav-i{
border-radius: 10px;
100px;
max-height: 50px;
float: left;
text-align: center;
line-height: 50px;
overflow: hidden; /*超出部分隐藏*/
}
.nav-i:hover{
border-radius: 10px;
background-color: antiquewhite;
cursor: pointer;
max-height: 500px;
transition: 0.5s;/*动画*/
}
.nav-i:li{
opacity: 0.5 ;
}
.nav-ii li{
border-radius: 10px;
height: 50px;
line-height: 50px;
text-align: center;
background-color: #ADD8E6;
}
.nav-ii li:hover{
border-radius: 10px;
background-color: antiquewhite;
cursor: pointer;
}
</style>
</head>
<body>
<div id="nav-banner">
<div class="nav-i">首页</div>
<div class="nav-i">公司简介
<ul class="nav-ii">
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
</ul>
</div>
<div class="nav-i">产品展示
<ul class="nav-ii">
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
</ul></div>
<div class="nav-i">合作伙伴
<ul class="nav-ii">
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
</ul></div>
<div class="nav-i">联系方式
<ul class="nav-ii">
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
<li>aaaaaaaa</li>
</ul></div>
</div>
<div style="position: absolute;">1233466556623323</div>
</body>
</html>