代码示例：（标识：bs_utility_borders_rounded）
<!DOCTYPE html>
<html lang="en">
<head>
<title>Bootstrap 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/5.1.2/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/5.1.2/js/bootstrap.bundle.js"></script>
<style>
span {
display: inline-block;
width: 70px;
height: 70px;
margin: 6px;
background-color: #555;
}
</style>
</head>
<body>
<div class="p-4">
<h2>边框圆角</h2>
<p>请使用 rounded 类为元素添加圆角：</p>
<span class="rounded"></span>
<span class="rounded-top"></span>
<span class="rounded-end"></span>
<span class="rounded-bottom"></span>
<span class="rounded-start"></span>
<span class="rounded-circle"></span>
<span class="rounded-pill" style="width:130px"></span>
<span class="rounded-0"></span>
<span class="rounded-1"></span>
<span class="rounded-2"></span>
<span class="rounded-3"></span>
</div>
</body>
</html>
