在Bootstrap 4中使用border-white类来为元素设置白色边框。
<div class="test border border-white"> This has white border </div>
上面的测试类为元素设置样式，如下所示-
<style>
.test {
width: 120px;
height: 100px;
margin: 10px;
background: blue;
}
</style>让我们看一个在Bootstrap中实现border-white类的示例-
<!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>
<style>
.test {
width: 120px;
height: 100px;
margin: 10px;
background: blue;
}
</style>
</head>
<body>
<div class="container">
<h4>Two Rectangles</h4>
<div class="test border border-white">This has white border</div>
<div class="test border border-success">This has orange border</div>
</div>
</body>
</html>