``` <!DOCTYPE html>
<html>
<head>
<meta charset=utf-8>
<style type="text/css">
.box {
width: 100px;
height: 100px;
border: solid 1px black;
//子绝父相
position:relative;
}
.btn{
width: 20px;
height: 20px;
background-color: red;
//设定居中对齐
text-align:center;
//设定btn位置
position:absolute;
top:-10px;
right:-10px;
}
</style>
</head>
<body>
<div class='box'>
<div class='btn'>X</div>
</div>
<script type="text/javascript">
var btn = document.querySelector('.btn');
var box = document.querySelector('.box');
btn.onclick = function(){
// 点击btn后box隐藏
box.style.display='none';
}
</script>
</body>
</html>