使用btn-outline-warning类为Bootstrap 4按钮设置橙色轮廓，并指示警告操作。
以下包括按钮上的橙色轮廓-
<button type="button" class="btn btn-outline-warning"> Rejected </button>
该类的添加与添加到Bootstrap中任何元素的任何其他类一样。对于Bootstrap按钮，我使用了<button>元素。
您可以尝试运行以下代码来实现btn-outline-warning类-
<!DOCTYPE html> <html lang="en"> <head> <title>Bootstrap Example</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/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/4.1.0/js/bootstrap.min.js"></script> </head> <body> <h3>College Placements</h3> <ul class = "list-group"> <li class = "list-group-item">Selected Students</li> <li class = "list-group-item">Rejected Students</li> <li class = "list-group-item">Result Awaited</li> </ul> <p>List of selected and rejected students:</p> <button type="button" class="btn btn-outline-success">Selected</button> <button type="button" class="btn btn-outline-warning">Rejected</button> </body> </html>