在Bootstrap中使用.btn-outline-dark类在按钮上设置深色轮廓。
以下是带有深色轮廓的按钮的示例-
使用btn-outline-dark类将上述轮廓设置为按钮，如下所示-
<button type="button" class="btn btn-outline-dark">
Submit
</button>您可以尝试运行以下代码以实现btn-outline-dark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>
<div class="container">
<h4>Bootstrap 4</h4>
<p>Learning btn-outline-dark class usage:</p>
<button type="button" class="btn btn-outline-dark">Submit</button>
</div>
</body>
</html>