要设置绿色边框，请使用Bootstrap 4中的border-success类。
以下元素将具有绿色边框，因为我们已将<div>的类设置为border-success类-
<div class="mystyle border border-success"> Green border </div>
您可以尝试运行以下代码以将绿色边框设置为表示成功的元素-
<!DOCTYPE html>
<html>
<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>
<style>
.mystyle {
width: 150px;
height: 150px;
margin: 10px;
}
</style>
</head>
<body>
<div class="container">
<h2>Rectangle</h2>
<div class="mystyle border border-success">Green border</div>
</div>
</body>
</html>