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-
<!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>