使用灰色的Bootstrap 4按钮设置不太重要的内容
要在Bootstrap中设置不太重要的内容，请使用btn-outline-secondary类。
使用相同的类将轮廓应用于按钮，并应用绿色-
<button type="button" class="btn btn-outline-secondary"> Tools (Secondary Outline) </button>
上面，我将btn-outline-secondary类设置为在任何元素上设置的任何普通类，此处为按钮。
您可以尝试运行以下代码以了解如何设置灰色轮廓的Bootstrap按钮-
示例
<!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>
<h2>Web Tools</h2>
<p>The following are the Tools:</p>
<ul class = "list-group">
<li class = "list-group-item">JSON Editor</li>
<li class = "list-group-item">XML Editor</li>
</ul>
<p>For more, click below:</p>
<button type="button" class="btn btn-outline-secondary"> Tools (Secondary Outline)</button>
</body>
</html>