Bootstrap 4 Flex（弹性）布局
<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>效果：
<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>效果：
<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>效果：
<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 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> <p>.flex-fill 类强制设置各个弹性子元素的宽度是一样的:</p> <div class="d-flex mb-3"> <div class="p-2 flex-fill bg-info">Flex item 1</div> <div class="p-2 flex-fill bg-warning">Flex item 2</div> <div class="p-2 flex-fill bg-primary">Flex item 3</div> </div> <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>.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> <p>.mr-auto 类可以设置子元素右外边距为 auto，.ml-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 mr-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 ml-auto bg-primary">Flex item 3</div> </div>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。
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。*
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)。*
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)。*
