源代码 ：
点击运行
<!DOCTYPE html> <html> <head> <title>Bootstrap 实例</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/css/bootstrap.min.css"> <script src="https://cdn.staticfile.org/jquery/3.2.1/jquery.min.js"></script> <script src="https://cdn.staticfile.org/popper.js/1.15.0/umd/popper.min.js"></script> <script src="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script> </head> <body> <div class="container mt-3"> <h2>单独显示在头部</h2> <p>.align-self-*-start 类据不同屏幕设备，让单独一个子元素显示在头部。</p> <p>重置浏览器窗口大小，查看效果。 <strong>注意:</strong> align-self-stretch 是默认的。</p> <p><code>.align-self-start</code>:</p> <div class="d-flex bg-light" style="height:150px"> <div class="p-2 border">Flex item 1</div> <div class="p-2 border align-self-start">Flex item 2</div> <div class="p-2 border">Flex item 3</div> </div> <br> <p><code>.align-self-sm-start</code>:</p> <div class="d-flex bg-light" style="height:150px"> <div class="p-2 border">Flex item 1</div> <div class="p-2 border align-self-sm-start">Flex item 2</div> <div class="p-2 border">Flex item 3</div> </div> <br> <p><code>.align-self-md-start</code>:</p> <div class="d-flex bg-light" style="height:150px"> <div class="p-2 border">Flex item 1</div> <div class="p-2 border align-self-md-start">Flex item 2</div> <div class="p-2 border">Flex item 3</div> </div> <br> <p><code>.align-self-lg-start</code>:</p> <div class="d-flex bg-light" style="height:150px"> <div class="p-2 border">Flex item 1</div> <div class="p-2 border align-self-lg-start">Flex item 2</div> <div class="p-2 border">Flex item 3</div> </div> <br> <p><code>.align-self-xl-start</code>:</p> <div class="d-flex bg-light" style="height:150px"> <div class="p-2 border">Flex item 1</div> <div class="p-2 border align-self-xl-start">Flex item 2</div> <div class="p-2 border">Flex item 3</div> </div> <br> </div> </body> </html>
运行结果