在Bootstrap 4中使用border-secondary类为元素添加灰色边框。
将边框设置为-
<div class="test border border-secondary"> Gray border </div>
我已经为元素<div>设置了样式，如以下代码片段所示：
<style>
.test {
width: 200px;
height: 150px;
margin: 10px;
}
</style>您可以尝试运行以下代码以实现border-secondary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>
<style>
.test {
width: 200px;
height: 150px;
margin: 10px;
}
</style>
</head>
<body>
<div class="container">
<h2>Rectangle</h2>
<div class="test border border-secondary">Gray border</div>
</div>
</body>
</html>