Bootstrap 4 .flex-*-column类
在Bootstrap中使用.flex-*-列类在不同的屏幕尺寸上垂直显示flex项目：
将其垂直设置在小，中，大等屏幕尺寸上。让我们在中小尺寸的屏幕上看到它：
小屏幕尺寸
<p>不同屏幕尺寸的伸缩（小）</p> <div class="d-flex flex-sm-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>
中等屏幕尺寸
<p>不同屏幕尺寸的伸缩（中）</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>
以下是一个示例，该示例实现了我上面使用flex-*-column显示的内容-
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>
<div class="container mt-3">
<h2>Example</h2>
<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>不同屏幕尺寸的伸缩（小）</p>
<div class="d-flex flex-sm-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>不同屏幕尺寸的伸缩（中）</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>不同屏幕尺寸的伸缩（大）</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>