Bootstrap5 Flex（弹性）布局
Bootstrap5 通过 flex 类来控制页面的布局。
弹性盒子(flexbox)
Bootstrap 3 与 Bootstrap 4/5 最大的区别就是 Bootstrap 4/5 使用弹性盒子来布局，而不是使用浮动来布局。
弹性盒子是 CSS3 的一种新的布局模式，更适合响应式的设计，如果你还不了解 flex，可以阅读我们的 CSS3 弹性盒子(Flex Box) 教程
注意：IE9 及其以下版本不支持弹性盒子，所以如果你需要兼容 IE8-9，请使用 Bootstrap 3。
以下实例使用 d-flex 类创建一个弹性盒子容器，并设置三个弹性子元素：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>Flex</h2>
<p>使用 d-flex 类创建一个弹性盒子容器，并设置三个弹性子元素：</p>
<div class="d-flex p-3 bg-secondary text-white">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>创建显示在同一行上的弹性盒子容器可以使用 d-inline-flex 类:
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>行内 Flex</h2>
<p>创建显示在同一行上的弹性盒子容器可以使用 d-inline-flex 类:</p>
<div class="d-inline-flex p-3 bg-secondary text-white">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>水平方向
.flex-row 可以设置弹性子元素水平显示，这是默认的。
使用 .flex-row-reverse 类用于设置右对齐显示，即与 .flex-row 方向相反。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>水平方向</h2>
<p>使用 .flex-row 类设置弹性子元素水平显示：</p>
<div class="d-flex flex-row bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<p>.flex-row-reverse 设置右对齐方向:</p>
<div class="d-flex flex-row-reverse bg-secondary">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>垂直方向
.flex-column 类用于设置弹性子元素垂直方向显示, .flex-column-reverse 用于翻转子元素：
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>垂直方向</h2>
<p>.flex-column 类用于设置弹性子元素垂直方向显示：</p>
<div class="d-flex flex-column mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<p>.flex-column-reverse 类用于设置弹性子元素垂直方向翻转显示：</p>
<div class="d-flex flex-column-reverse">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>内容排列
.justify-content-* 类用于修改弹性子元素的排列方式，* 号允许的值有：start (默认), end, center, between 或 around:
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>Justify content</h2>
<p>.justify-content-* 类用于修改弹性子元素的排列方式，* 号允许的值有：start (默认), end, center, between 或 around:</p>
<div class="d-flex justify-content-start bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<div class="d-flex justify-content-end bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<div class="d-flex justify-content-center bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<div class="d-flex justify-content-between bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<div class="d-flex justify-content-around bg-secondary mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>等宽
.flex-fill 类强制设置各个弹性子元素的宽度是一样的:
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>等宽</h2>
<p>.flex-fill 用于设置子元素等宽：</p>
<div class="d-flex">
<div class="p-2 bg-info flex-fill">Flex item 1</div>
<div class="p-2 bg-warning flex-fill">Flex item 2</div>
<div class="p-2 bg-primary flex-fill">Flex item 3</div>
</div>
</div>
</body>
</html>扩展
.flex-grow-1 用于设置子元素使用剩下的空间。以下实例中前面两个子元素只设置了它们所需要的空间，最后一个获取剩余空间。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>扩展</h2>
<p>.flex-grow-1 用于设置子元素使用剩下的空间：</p>
<div class="d-flex mb-3">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 flex-grow-1 bg-primary">Flex item 3</div>
</div>
<p>不使用 .flex-grow-1 实例:</p>
<div class="d-flex mb-3 bg-secondary">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>提示: 使用 .flex-shrink-1 用于设置子元素的收缩规则。
排序
.order 类可以设置弹性子元素的排序，从 .order-1 到 .order-12，数字越低权重越高( .order-1 排在 .order-2 之前) :
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>排序</h2>
<p>.order 类可以设置弹性子元素的排序，从 .order-1 到 .order-12，数字越低权重越高:</p>
<div class="d-flex mb-3">
<div class="p-2 order-3 bg-info">Flex item 1</div>
<div class="p-2 order-2 bg-warning">Flex item 2</div>
<div class="p-2 order-1 bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>外边距
.ms-auto 类可以设置子元素右外边距为 auto，即 margin-right: auto!important;，.me-auto 类可以设置子元素左外边距为 auto，即 margin-left: auto!important;:
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>外边距</h2>
<p>.ms-auto 类可以设置子元素右外边距为 auto，.me-auto 类可以设置子元素左外边距为 auto:</p>
<div class="d-flex mb-3 bg-secondary">
<div class="p-2 ms-auto bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 bg-primary">Flex item 3</div>
</div>
<div class="d-flex mb-3 bg-secondary">
<div class="p-2 bg-info">Flex item 1</div>
<div class="p-2 bg-warning">Flex item 2</div>
<div class="p-2 me-auto bg-primary">Flex item 3</div>
</div>
</div>
</body>
</html>包裹
弹性容器中包裹子元素可以使用以下三个类： .flex-nowrap (默认), .flex-wrap 或 .flex-wrap-reverse。设置 flex 容器是单行或者多行。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>包裹</h2>
<p>弹性容器中包裹弹性子元素可以使用以下三个类： .flex-nowrap (默认), .flex-wrap 或 .flex-wrap-reverse:</p>
<p><code>.flex-wrap:</code></p>
<div class="d-flex flex-wrap bg-light">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p><code>.flex-wrap-reverse:</code></p>
<div class="d-flex flex-wrap-reverse bg-light">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p><code>.flex-nowrap:</code></p>
<div class="d-flex flex-nowrap bg-light">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
<div class="p-2 border">Flex item 26</div>
<div class="p-2 border">Flex item 27</div>
<div class="p-2 border">Flex item 28</div>
<div class="p-2 border">Flex item 29</div>
<div class="p-2 border">Flex item 30</div>
<div class="p-2 border">Flex item 31</div>
<div class="p-2 border">Flex item 32</div>
<div class="p-2 border">Flex item 33</div>
<div class="p-2 border">Flex item 34</div>
<div class="p-2 border">Flex item 35</div>
</div>
<br>
</div>
</body>
</html>内容对齐
我们可以使用 .align-content-* 来控制在垂直方向上如何去堆叠子元素，包含的值有：.align-content-start (默认), .align-content-end, .align-content-center, .align-content-between, .align-content-around 和 .align-content-stretch。
这些类在只有一行的弹性子元素中是无效的。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>内容对齐</h2>
<p>我们可以使用 .align-content-* 来控制子元素在垂直方向的对齐方式。</p>
<p><strong>注意:</strong> 这个实例在小型设备上效果不好。这些类在只有一行的弹性子元素中是无效的。</p>
<p>.align-content-start (默认):</p>
<div class="d-flex flex-wrap align-content-start bg-light" style="height:300px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p>.align-content-end:</p>
<div class="d-flex flex-wrap align-content-end bg-light" style="height:300px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p>.align-content-center:</p>
<div class="d-flex flex-wrap align-content-center bg-light" style="height:300px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p>.align-content-around:</p>
<div class="d-flex flex-wrap align-content-around bg-light" style="height:300px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
<p>.align-content-stretch:</p>
<div class="d-flex flex-wrap align-content-stretch bg-light" style="height:300px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
<div class="p-2 border">Flex item 4</div>
<div class="p-2 border">Flex item 5</div>
<div class="p-2 border">Flex item 6</div>
<div class="p-2 border">Flex item 7</div>
<div class="p-2 border">Flex item 8</div>
<div class="p-2 border">Flex item 9</div>
<div class="p-2 border">Flex item 10</div>
<div class="p-2 border">Flex item 11</div>
<div class="p-2 border">Flex item 12</div>
<div class="p-2 border">Flex item 13 </div>
<div class="p-2 border">Flex item 14</div>
<div class="p-2 border">Flex item 15</div>
<div class="p-2 border">Flex item 16</div>
<div class="p-2 border">Flex item 17</div>
<div class="p-2 border">Flex item 18</div>
<div class="p-2 border">Flex item 19</div>
<div class="p-2 border">Flex item 20</div>
<div class="p-2 border">Flex item 21</div>
<div class="p-2 border">Flex item 22</div>
<div class="p-2 border">Flex item 23</div>
<div class="p-2 border">Flex item 24</div>
<div class="p-2 border">Flex item 25</div>
</div>
<br>
</div>
</body>
</html>子元素对齐
如果要设置单行的子元素对齐可以使用 .align-items-* 类来控制，包含的值有：.align-items-start, .align-items-end, .align-items-center, .align-items-baseline, 和 .align-items-stretch (默认)。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>子元素对齐</h2>
<p>如果要设置单行的子元素对齐可以使用 .align-content-* 类来控制。</p>
<p>.align-items-start:</p>
<div class="d-flex align-items-start bg-light" style="height:150px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-items-end:</p>
<div class="d-flex align-items-end bg-light" style="height:150px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-items-center:</p>
<div class="d-flex align-items-center bg-light" style="height:150px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-items-baseline:</p>
<div class="d-flex align-items-baseline bg-light" style="height:150px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-items-stretch (默认):</p>
<div class="d-flex align-items-stretch bg-light" style="height:150px">
<div class="p-2 border">Flex item 1</div>
<div class="p-2 border">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
</div>
</body>
</html>指定子元素对齐
如果要设置指定子元素对齐对齐可以使用 .align-self-* 类来控制，包含的值有：.align-self-start, .align-self-end, .align-self-center, .align-self-baseline, 和 .align-self-stretch (默认)。
<!DOCTYPE html>
<html>
<head>
<title>Bootstrap5 实例</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://cdn.staticfile.org/twitter-bootstrap/5.1.1/js/bootstrap.bundle.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>Align Self</h2>
<p>如果要设置指定子元素对齐对齐可以使用 .align-self-* 类来控制。</p>
<p>.align-self-start:</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>.align-self-end:</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-end">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-self-center:</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-center">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-self-baseline:</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-baseline">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
<p>.align-self-stretch (默认):</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-stretch">Flex item 2</div>
<div class="p-2 border">Flex item 3</div>
</div>
<br>
</div>
</body>
</html>响应式 flex 类
我们可以根据不同的设备，设置 flex 类，从而实现页面响应式布局，以下表格中的 * 号可以的值有：sm, md, lg 或 xl, 对应的是小型设备、中型设备，大型设备，超大型设备。
| 类 | 实例 |
|---|---|
| 弹性容器 | |
.d-*-flex
|
根据不同的屏幕设备创建弹性盒子容器 |
.d-*-inline-flex
|
根据不同的屏幕设备创建行内弹性盒子容器 |
| 方向 | |
.flex-*-row
|
根据不同的屏幕设备在水平方向显示弹性子元素 |
.flex-*-row-reverse
|
根据不同的屏幕设备在水平方向显示弹性子元素，且右对齐 |
.flex-*-column
|
根据不同的屏幕设备在垂直方向显示弹性子元素 |
.flex-*-column-reverse
|
根据不同的屏幕设备在垂直方向显示弹性子元素，且方向相反 |
| 内容对齐 | |
.justify-content-*-start
|
根据不同屏幕设备在开始位置显示弹性子元素 (左对齐) |
.justify-content-*-end
|
根据不同屏幕设备在尾部显示弹性子元素 (右对齐) |
.justify-content-*-center
|
根据不同屏幕设备在 flex 容器中居中显示子元素 |
.justify-content-*-between
|
根据不同屏幕设备使用 "between" 显示弹性子元素 |
.justify-content-*-around
|
根据不同屏幕设备使用 "around" 显示弹性子元素 |
| 等宽 | |
.flex-*-fill
|
根据不同的屏幕设备强制等宽 |
| 扩展 | |
.flex-*-grow-0
|
不同的屏幕设备不设置扩展 |
.flex-*-grow-1
|
不同的屏幕设备设置扩展 |
| 收缩 | |
.flex-*-shrink-0
|
不同的屏幕设备不设置收缩 |
.flex-*-shrink-1
|
不同的屏幕设备设置收缩 |
| 包裹 | |
.flex-*-nowrap
|
不同的屏幕设备不设置包裹元素 |
.flex-*-wrap
|
不同的屏幕设备设置包裹元素 |
.flex-*-wrap-reverse
|
不同的屏幕设备反转包裹元素 |
| 内容排列 | |
.align-content-*-start
|
根据不同屏幕设备在起始位置堆叠元素 |
.align-content-*-end
|
根据不同屏幕设备在结束位置堆叠元素 |
.align-content-*-center
|
根据不同屏幕设备在中间位置堆叠元素 |
.align-content-*-around
|
根据不同屏幕设备，使用 "around" 堆叠元素 |
.align-content-*-stretch
|
根据不同屏幕设备，通过伸展元素来堆叠 |
| 排序 | |
.order-*-0-12
|
在小屏幕尺寸上修改排序 |
| 元素对齐 | |
.align-items-*-start
|
根据不同屏幕设备，让元素在头部显示在同一行。 |
.align-items-*-end
|
根据不同屏幕设备，让元素在尾部显示在同一行。 |
.align-items-*-center
|
根据不同屏幕设备，让元素在中间位置显示在同一行。 |
.align-items-*-baseline
|
根据不同屏幕设备，让元素在基线上显示在同一行。 |
.align-items-*-stretch
|
根据不同屏幕设备，让元素延展高度并显示在同一行。 |
| 单独一个子元素的对齐方式 | |
.align-self-*-start
|
据不同屏幕设备，让单独一个子元素显示在头部。 |
.align-self-*-end
|
据不同屏幕设备，让单独一个子元素显示在尾部 |
.align-self-*-center
|
据不同屏幕设备，让单独一个子元素显示在居中位置 |
.align-self-*-baseline
|
据不同屏幕设备，让单独一个子元素显示在基线位置 |
.align-self-*-stretch
|
据不同屏幕设备，延展一个单独子元素 |