向元素添加黄色背景色以使用Bootstrap设置警告操作
要将警告动作设置为Bootstrap中的按钮，请使用.btn-warning按钮。您可以尝试运行以下代码来实现btn-warning按钮
示例
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap Example</title>
<link rel = "stylesheet" href = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css">
<script src = "https://cdn.staticfile.org/jquery/3.3.1/jquery.min.js"></script>
<script src = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
</head>
<body>
<p>Click below if you want to know the warning message:</p>
<button type = "button" class = "btn btn-warning">Warning</button>
</body>
</html>