弹性（Flex）
借助一整套响应式Flexbox实用工具，快速管理网格列，导航，组件等布局，对齐和大小。对于更复杂的实现，可能需要自定义CSS。
启用弹性行为
应用display实用程序来创建一个flexbox容器，并将直接子元素转换为flex。Flex容器和项目可以通过其他的flex属性进行进一步修改。
<div class="d-flex p-2 bd-highlight">I'm a flexbox container!</div>
<div class="d-inline-flex p-2 bd-highlight">I'm an inline flexbox container!</div>
.d-flex和.d-inline-flex也存在响应式变化。
.d-flex.d-inline-flex.d-sm-flex.d-sm-inline-flex.d-md-flex.d-md-inline-flex.d-lg-flex.d-lg-inline-flex.d-xl-flex.d-xl-inline-flex.d-xxl-flex.d-xxl-inline-flex
方向
通过方向工具设置flex容器中flex项的方向。在大多数情况下，你可以省略这里的水平类（horizontal），因为浏览器的默认值是row。但是，你可能会遇到需要明确设置该值的情况（如响应式布局）。
使用.flex-row来设置水平方向（浏览器默认），或使用.flex-row-reverse从相反的一侧开始水平方向。
<div class="d-flex flex-row bd-highlight mb-3">
<div class="p-2 bd-highlight">Flex item 1</div>
<div class="p-2 bd-highlight">Flex item 2</div>
<div class="p-2 bd-highlight">Flex item 3</div>
</div>
<div class="d-flex flex-row-reverse bd-highlight">
<div class="p-2 bd-highlight">Flex item 1</div>
<div class="p-2 bd-highlight">Flex item 2</div>
<div class="p-2 bd-highlight">Flex item 3</div>
</div>
使用.flex-column设置垂直方向，或.flex-column-reverse从反面开始垂直方向。
<div class="d-flex flex-column bd-highlight mb-3">
<div class="p-2 bd-highlight">Flex item 1</div>
<div class="p-2 bd-highlight">Flex item 2</div>
<div class="p-2 bd-highlight">Flex item 3</div>
</div>
<div class="d-flex flex-column-reverse bd-highlight">
<div class="p-2 bd-highlight">Flex item 1</div>
<div class="p-2 bd-highlight">Flex item 2</div>
<div class="p-2 bd-highlight">Flex item 3</div>
</div>
flex-direction也有响应的变化。
.flex-row.flex-row-reverse.flex-column.flex-column-reverse.flex-sm-row.flex-sm-row-reverse.flex-sm-column.flex-sm-column-reverse.flex-md-row.flex-md-row-reverse.flex-md-column.flex-md-column-reverse.flex-lg-row.flex-lg-row-reverse.flex-lg-column.flex-lg-column-reverse.flex-xl-row.flex-xl-row-reverse.flex-xl-column.flex-xl-column-reverse.flex-xxl-row.flex-xxl-row-reverse.flex-xxl-column.flex-xxl-column-reverse
对齐内容（Justify content）
在flexbox容器上使用justify-content来更改flex项目在主轴上的对齐方式（x轴开始，y轴，如果是flex-direction：column）。从start（浏览器默认），end、center、between、around或evenly中选择。
<div class="d-flex justify-content-start">...</div>
<div class="d-flex justify-content-end">...</div>
<div class="d-flex justify-content-center">...</div>
<div class="d-flex justify-content-between">...</div>
<div class="d-flex justify-content-around">...</div>
<div class="d-flex justify-content-evenly">...</div>
justify-content也有响应的变化。
.justify-content-start.justify-content-end.justify-content-center.justify-content-between.justify-content-around.justify-content-evenly.justify-content-sm-start.justify-content-sm-end.justify-content-sm-center.justify-content-sm-between.justify-content-sm-around.justify-content-sm-evenly.justify-content-md-start.justify-content-md-end.justify-content-md-center.justify-content-md-between.justify-content-md-around.justify-content-md-evenly.justify-content-lg-start.justify-content-lg-end.justify-content-lg-center.justify-content-lg-between.justify-content-lg-around.justify-content-lg-evenly.justify-content-xl-start.justify-content-xl-end.justify-content-xl-center.justify-content-xl-between.justify-content-xl-around.justify-content-xl-evenly.justify-content-xxl-start.justify-content-xxl-end.justify-content-xxl-center.justify-content-xxl-between.justify-content-xxl-around.justify-content-xxl-evenly
对齐items
在flexbox容器上使用align-items来更改flex items在横轴上的对齐方式（y轴开始，x轴为flex-direction：column）。从start，end, center, baseline或stretch中选择（浏览器默认）。
<div class="d-flex align-items-start">...</div>
<div class="d-flex align-items-end">...</div>
<div class="d-flex align-items-center">...</div>
<div class="d-flex align-items-baseline">...</div>
<div class="d-flex align-items-stretch">...</div>
align-items也有响应的变化。
.align-items-start.align-items-end.align-items-center.align-items-baseline.align-items-stretch.align-items-sm-start.align-items-sm-end.align-items-sm-center.align-items-sm-baseline.align-items-sm-stretch.align-items-md-start.align-items-md-end.align-items-md-center.align-items-md-baseline.align-items-md-stretch.align-items-lg-start.align-items-lg-end.align-items-lg-center.align-items-lg-baseline.align-items-lg-stretch.align-items-xl-start.align-items-xl-end.align-items-xl-center.align-items-xl-baseline.align-items-xl-stretch.align-items-xxl-start.align-items-xxl-end.align-items-xxl-center.align-items-xxl-baseline.align-items-xxl-stretch
自我对齐（Align self）
在flexbox项目上使用align-self可分别更改其在横轴上的对齐方式（y轴开始，x轴为flex-direction：column）。从与align-items相同的选项中进行选择：start，end，center，baseline或stretch（浏览器默认）。
<div class="align-self-start">Aligned flex item</div>
<div class="align-self-end">Aligned flex item</div>
<div class="align-self-center">Aligned flex item</div>
<div class="align-self-baseline">Aligned flex item</div>
<div class="align-self-stretch">Aligned flex item</div>
align-self也有响应的变化。
.align-self-start.align-self-end.align-self-center.align-self-baseline.align-self-stretch.align-self-sm-start.align-self-sm-end.align-self-sm-center.align-self-sm-baseline.align-self-sm-stretch.align-self-md-start.align-self-md-end.align-self-md-center.align-self-md-baseline.align-self-md-stretch.align-self-lg-start.align-self-lg-end.align-self-lg-center.align-self-lg-baseline.align-self-lg-stretch.align-self-xl-start.align-self-xl-end.align-self-xl-center.align-self-xl-baseline.align-self-xl-stretch.align-self-xxl-start.align-self-xxl-end.align-self-xxl-center.align-self-xxl-baseline.align-self-xxl-stretch
填充
在一系列的同级元素上使用.flex-fill类，以使它们的宽度与它们的内容相等（如果它们的内容没有超过它们的边框，则宽度相等），同时占用所有可用的水平空间。
<div class="d-flex bd-highlight">
<div class="p-2 flex-fill bd-highlight">Flex item with a lot of content</div>
<div class="p-2 flex-fill bd-highlight">Flex item</div>
<div class="p-2 flex-fill bd-highlight">Flex item</div>
</div>
flex-fill也有响应的变化。
.flex-fill.flex-sm-fill.flex-md-fill.flex-lg-fill.flex-xl-fill.flex-xxl-fill
增长和收缩
使用.flex-grow-*来切换弹性项目（flex item）增长以填充可用空间的能力。 在下面的示例中，.flex-grow-1元素将使用其所有可能的可用空间，同时为其余两个flex项目提供必要的空间。
<div class="d-flex bd-highlight">
<div class="p-2 flex-grow-1 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Third flex item</div>
</div>
如果需要的话，使用.flex-shrink-*实用程序来切换弹性item的收缩能力。在下面的例子中，第二个带有.flex-shrink-1的弹性item被迫将其内容包到新的行中，“shrinking” 以使前一个带有.w-100的弹性item有更多空间。
<div class="d-flex bd-highlight">
<div class="p-2 w-100 bd-highlight">Flex item</div>
<div class="p-2 flex-shrink-1 bd-highlight">Flex item</div>
</div>
flex-grow和 flex-shrink也有响应的变化。
.flex-{grow|shrink}-0.flex-{grow|shrink}-1.flex-sm-{grow|shrink}-0.flex-sm-{grow|shrink}-1.flex-md-{grow|shrink}-0.flex-md-{grow|shrink}-1.flex-lg-{grow|shrink}-0.flex-lg-{grow|shrink}-1.flex-xl-{grow|shrink}-0.flex-xl-{grow|shrink}-1.flex-xxl-{grow|shrink}-0.flex-xxl-{grow|shrink}-1
自动margins
当将弹性对齐和自动边距混合在一起时，Flexbox可以做一些非常棒的事情。下面显示的是通过自动边距控制flex项的三个例子：默认（无自动边距），向右推两个项（.mr-auto），向左推两个项（.ml-auto）。
<div class="d-flex bd-highlight mb-3">
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
</div>
<div class="d-flex bd-highlight mb-3">
<div class="mr-auto p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
</div>
<div class="d-flex bd-highlight mb-3">
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="ml-auto p-2 bd-highlight">Flex item</div>
</div>
与align-items
通过混合对齐项，flex-direction：column和margin-top：auto或margin-bottom：auto，将一个flex项目垂直移动到容器的顶部或底部。
<div class="d-flex align-items-start flex-column bd-highlight mb-3" style="height: 200px;">
<div class="mb-auto p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
</div>
<div class="d-flex align-items-end flex-column bd-highlight mb-3" style="height: 200px;">
<div class="p-2 bd-highlight">Flex item</div>
<div class="p-2 bd-highlight">Flex item</div>
<div class="mt-auto p-2 bd-highlight">Flex item</div>
</div>
包裹（Wrap）
改变flex项目在flex容器中的包装方式。可以选择.flex-nowrap完全不包裹（浏览器默认），.flex-wrap包裹换行，或者.flex-wrap-reverse反向包裹。
<div class="d-flex flex-nowrap">
...
</div>
<div class="d-flex flex-wrap">
...
</div>
<div class="d-flex flex-wrap-reverse">
...
</div>
flex-wrap也有响应式的变化。
.flex-nowrap.flex-wrap.flex-wrap-reverse.flex-sm-nowrap.flex-sm-wrap.flex-sm-wrap-reverse.flex-md-nowrap.flex-md-wrap.flex-md-wrap-reverse.flex-lg-nowrap.flex-lg-wrap.flex-lg-wrap-reverse.flex-xl-nowrap.flex-xl-wrap.flex-xl-wrap-reverse.flex-xxl-nowrap.flex-xxl-wrap.flex-xxl-wrap-reverse
顺序
使用少量的order来改变特定flex项目的显示顺序。我们只提供了让一个item排在第一位或最后一位的选项，以及使用DOMorder的重置选项。由于order可以取0到5的任何整数值，因此可以为任何需要的额外值添加自定义CSS。
<div class="d-flex flex-nowrap bd-highlight">
<div class="order-3 p-2 bd-highlight">First flex item</div>
<div class="order-2 p-2 bd-highlight">Second flex item</div>
<div class="order-1 p-2 bd-highlight">Third flex item</div>
</div>
Responsive variations also exist for order.
.order-0.order-1.order-2.order-3.order-4.order-5.order-sm-0.order-sm-1.order-sm-2.order-sm-3.order-sm-4.order-sm-5.order-md-0.order-md-1.order-md-2.order-md-3.order-md-4.order-md-5.order-lg-0.order-lg-1.order-lg-2.order-lg-3.order-lg-4.order-lg-5.order-xl-0.order-xl-1.order-xl-2.order-xl-3.order-xl-4.order-xl-5.order-xxl-0.order-xxl-1.order-xxl-2.order-xxl-3.order-xxl-4.order-xxl-5
Additionally there are also responsive .order-first and .order-last classes that change the order of an element by applying order: -1 and order: 6, respectively.
.order-first.order-last.order-sm-first.order-sm-last.order-md-first.order-md-last.order-lg-first.order-lg-last.order-xl-first.order-xl-last.order-xxl-first.order-xxl-last
Align content
Use align-content utilities on flexbox containers to align flex items together on the cross axis. Choose from start (browser default), end, center, between, around, or stretch. To demonstrate these utilities, we’ve enforced flex-wrap: wrap and increased the number of flex items.
Heads up! This property has no effect on single rows of flex items.
<div class="d-flex align-content-start flex-wrap">
...
</div>
<div class="d-flex align-content-end flex-wrap">...</div>
<div class="d-flex align-content-center flex-wrap">...</div>
<div class="d-flex align-content-between flex-wrap">...</div>
<div class="d-flex align-content-around flex-wrap">...</div>
<div class="d-flex align-content-stretch flex-wrap">...</div>
Responsive variations also exist for align-content.
.align-content-start.align-content-end.align-content-center.align-content-around.align-content-stretch.align-content-sm-start.align-content-sm-end.align-content-sm-center.align-content-sm-around.align-content-sm-stretch.align-content-md-start.align-content-md-end.align-content-md-center.align-content-md-around.align-content-md-stretch.align-content-lg-start.align-content-lg-end.align-content-lg-center.align-content-lg-around.align-content-lg-stretch.align-content-xl-start.align-content-xl-end.align-content-xl-center.align-content-xl-around.align-content-xl-stretch.align-content-xxl-start.align-content-xxl-end.align-content-xxl-center.align-content-xxl-around.align-content-xxl-stretch
Media object
Looking to replicate the media object component from Bootstrap 4? Recreate it in no time with a few flex utilities that allow even more flexibility and customization than before.
<div class="d-flex">
<div class="flex-shrink-0">
<img src="..." alt="...">
</div>
<div class="flex-grow-1 ms-3">
This is some content from a media component. You can replace this with any content and adjust it as needed.
</div>
</div>
<div class="d-flex align-items-center">
<div class="flex-shrink-0">
<img src="..." alt="...">
</div>
<div class="flex-grow-1 ms-3">
This is some content from a media component. You can replace this with any content and adjust it as needed.
</div>
</div>
