####### 3、 推荐一个css网址 https://www.zhangxinxu.com/wordpress/
这样就是一个展开收缩的效果了<body>
<div id="div1">
<ul>
<li></li>
</ul>
</div>
<script>
var oDiv = document.getElementById('div1')
var oUl = oDiv.getElementsByTagName('ul')[0]
var Off = true
oDiv.onclick = function(){
if(Off){
oUl.style.display = "block"
Off = false
}else{
oUl.style.display = "none"
Off = true
}
}
</script>