需要用到的知识就是box-shadow , 和 outline 实现多重边框
实现这样的效果
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
.dd {
position: absolute;
left: 400px;
top: 200px;
width: calc(100% - 800px);
height: calc(100% - 400px);
background: lawngreen;
border-radius: 50px;
box-shadow: 0 0 0 30px #665555;
outline: 50px solid #665555;
}
</style>
</head>
<body>
<div class="dd">
</div>
</body>
</html>
原文：https://www.cnblogs.com/lilei-site/p/11785466.html