bootstrap4 在线编辑器 | bootstrap4代码测试

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Bootstrap 示例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://www.cainiaomax.com/lib/bootstrap/4.5.2/css/bootstrap.min.css">
  <script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.5.1.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.0/umd/popper.min.js"></script>
  <script src="https://www.cainiaomax.com/lib/bootstrap/4.5.2/js/bootstrap.min.js"></script>
</head>
<body>

<div class="container">
  <h2>通过 JavaScript 关闭警报</h2>
  <div class="alert alert-success alert-dismissible" id="myAlert">
    <button type="button" class="close">&times;</button>
    <strong>你好！</strong>尝试关闭此警告消息。
  </div>
</div>

</body>
</html>

报个问题: