CSS下拉动画：
<head>
<style>
*{
margin:0px
height:0px
list-st
.top-nav{
800
height:40
margin:0px auto;
background-color:***
}
.nav-btn-1v1{
500
<body>
<div class="top-container">
<div class="top-nav">
<div class="nav-btn-1v1">导航</div>
<div class="nav-btn-1v1">导航</div>
<div class="nav-btn-1v1">导航</div>
<div class="nav-btn-1v1">导航</div>
</div>