<!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.jsdelivr.net/npm/bootstrap@5.1.2/dist/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.2/dist/js/bootstrap.bundle.min.js"></script>
<style>
span { display: inline-block;
width: 70px;
height: 70px;
margin: 6px;
background-color: #f9f9f9;
}
</style>
</head>
<body>
<div class="container mt-3">
<h2>边框</h2>
<p>使用边框类为元素添加或删除边框：</p>
<span class="border"></span>
<span class="border border-0"></span>
<span class="border border-top-0"></span>
<span class="border border-end-0"></span>
<span class="border border-bottom-0"></span>
<span class="border border-start-0"></span>
<br>
<span class="border-top"></span>
<span class="border-end"></span>
<span class="border-bottom"></span>
<span class="border-start"></span>
</div>
</body>
</html>