Bootstrap 4 .d-*-flex类
使用Bootstrap中的.d-*-flex类在屏幕尺寸上设置flexbox容器，如下所示-
<div class="d-flex bg-primary">d-flex</div> <span class="d-sm-flex bg-warning">d-sm-flex</span> <span class="d-md-flex bg-info">d-md-flex</span> <span class="d-lg-flex bg-success">d-lg-flex</span>
在flex上方设置了不同的屏幕尺寸，例如，
d-md-flex=适用于中屏幕尺寸的Flex
d-lg-flex =适用于大屏幕尺寸的Flex
d-xl-flex =适用于超大屏幕尺寸的Flex
让我们看一个类的例子-
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>Understanding Flex</h2>
<div class="d-flex bg-primary">d-flex</div>
<span class="d-sm-flex bg-warning">Small Screen Size</span>
<span class="d-md-flex bg-info"> Medium Screen Size </span>
<span class="d-lg-flex bg-success"> Large Screen Size </span>
<span class="d-xl-flex bg-danger"> Extra Large Screen Size </span>
</div>
</body>
</html>