在Bootstrap 4中以不同的屏幕尺寸垂直显示flex项目
要在不同的屏幕尺寸上垂直显示弹性项目，请使用flex-*-列类。对于小，中和大屏幕尺寸，将其用作-
对于小屏幕尺寸-
<div class="d-flex flex-sm-column mb-3">
对于中等屏幕尺寸-
<div class="d-flex flex-md-column mb-3">
对于大屏幕尺寸-
<div class="d-flex flex-lg-column mb-3">
让我们看一个示例，以学习如何在不同的屏幕尺寸上垂直设置弹性项目-
示例
<!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>
</head>
<body>
<div class="container mt-3">
<h2>Example</h2>
<p>Note: Change the browser size to see the effect.</p>
<p>Default </p>
<div class="d-flex flex-column mb-3">
<div class="p-2 bg-primary">One</div>
<div class="p-2 bg-secondary">Two</div>
<div class="p-2 bg-info">Three</div>
</div>
<p>Flex on differet screen size (Medium)</p>
<div class="d-flex flex-md-column mb-3">
<div class="p-2 bg-warning">One</div>
<div class="p-2 bg-danger">Two</div>
<div class="p-2 bg-secondary">Three</div>
</div>
<p>Flex on differet screen size (Large)</p>
<div class="d-flex flex-lg-column mb-3">
<div class="p-2 bg-primary">One</div>
<div class="p-2 bg-secondary">Two</div>
<div class="p-2 bg-danger">Three</div>
</div>
</div>
</body>
</html>