弹性（Flex）

启用Flex行为

应用display 实用程序来创建弹性框容器，并将直接子元素转换为flex项。可以使用其他 flex 属性进一步修改 Flex 容器和项。

<div class="d-flex p-2">I'm a flexbox container!</div>

<div class="d-inline-flex p-2">I'm an inline flexbox container!</div>

.d-flex和.d-inline-flex也存在响应式变体。

• .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

使用方向实用程序在flex 容器中设置 flex 项的方向。在大多数情况下，您可以在此处省略水平类，因为浏览器默认值为row。但是，您可能会遇到需要显式设置此值（如响应式布局）的情况。

使用.flex-row设置水平方向（浏览器默认值），或使用.flex-row-reverse从另一侧开始水平方向。

<div class="d-flex flex-row mb-3">
  <div class="p-2">Flex item 1</div>
  <div class="p-2">Flex item 2</div>
  <div class="p-2">Flex item 3</div>
</div>
<div class="d-flex flex-row-reverse">
  <div class="p-2">Flex item 1</div>
  <div class="p-2">Flex item 2</div>
  <div class="p-2">Flex item 3</div>
</div>

使用.flex-column设置垂直方向，或使用.flex-column-reverse从另一侧开始垂直方向。

<div class="d-flex flex-column mb-3">
  <div class="p-2">Flex item 1</div>
  <div class="p-2">Flex item 2</div>
  <div class="p-2">Flex item 3</div>
</div>
<div class="d-flex flex-column-reverse">
  <div class="p-2">Flex item 1</div>
  <div class="p-2">Flex item 2</div>
  <div class="p-2">Flex item 3</div>
</div>

flex-direction也存在响应式变体。

• .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

两端对齐内容 (justify content)

使用 flexbox 容器上的 justify-content实用程序来更改主轴上flex项的对齐方式（x 轴开始，如果为flex-direction: column，则为 y 轴）。从 start（浏览器默认）、 end、center、between、 around或evenly中进行选择。

<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也存在响应式变体。

• .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

对齐项

使用 flexbox 容器上的 align-items实用程序来更改交叉轴上flex项的对齐方式（从 y 轴开始，如果为flex-direction: column，则为 x 轴）。从start、 end、 center、 baseline或stretch（浏览器默认）中进行选择。

<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也存在响应式变体。

• .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

在flex项上使用align-self实用程序以单独更改它们在十字轴上的对齐方式（从 y 轴开始，如果为flex-direction: column，则为 x 轴）。从与align-items相同的选项中进行选择： start, end, center, baseline或stretch（浏览器默认设置）。

<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也存在响应变体。

• .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 (Fill)

在一系列同级元素上使用.flex-fill类，强制它们宽度等于其内容（如果内容不超过边框框，则宽度相等），同时占用所有可用的水平空间。

<div class="d-flex">
  <div class="p-2 flex-fill">Flex item with a lot of content</div>
  <div class="p-2 flex-fill">Flex item</div>
  <div class="p-2 flex-fill">Flex item</div>
</div>

flex-fill也存在响应式变体。

• .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-*实用程序切换flex项的增长能力以填充可用空间。在下面的示例中，.flex-grow-1元素使用它所能使用的所有可用空间，同时允许其余两个 flex 项提供必要的空间。

<div class="d-flex">
  <div class="p-2 flex-grow-1">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="p-2">Third flex item</div>
</div>

如有必要，使用.flex-shrink-*实用程序切换flex项收缩功能。在下面的示例中，带有.flex-shrink-1 的第二个flex项被迫将其内容包装到一个新行“收缩”，以便为带有.w-100的上一个flex项留出更多空间。

<div class="d-flex">
  <div class="p-2 w-100">Flex item</div>
  <div class="p-2 flex-shrink-1">Flex item</div>
</div>

flex-grow和flex-shrink也存在响应变体。

• .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

自动边距

当您将弹性对齐与自动边距混合时，Flexbox 可以做一些非常棒的事情。下面显示了通过自动边距控制flex项的三个示例：默认（无自动边距）、向右推送两个项（.me-auto）和向左推送两个项（.ms-auto）。

<div class="d-flex mb-3">
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
</div>

<div class="d-flex mb-3">
  <div class="me-auto p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
</div>

<div class="d-flex mb-3">
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="ms-auto p-2">Flex item</div>
</div>

使用对齐项

通过混合align-items、flex-direction: column和margin-top: auto或margin-bottom: auto，垂直将一个flex项移动到容器的顶部或底部。

<div class="d-flex align-items-start flex-column mb-3" style="height: 200px;">
  <div class="mb-auto p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
</div>

<div class="d-flex align-items-end flex-column mb-3" style="height: 200px;">
  <div class="p-2">Flex item</div>
  <div class="p-2">Flex item</div>
  <div class="mt-auto p-2">Flex item</div>
</div>

包装(Wrap)

更改flex项在弹性容器中的包装方式。从完全不使用包装（浏览器默认设置）使用.flex-nowrap、使用.flex-wrap进行包装或使用.flex-wrap-reverse进行反向包装中进行选择。

<div class="d-flex flex-nowrap">
  ...
</div>

<div class="d-flex flex-wrap">
  ...
</div>

<div class="d-flex flex-wrap-reverse">
  ...
</div>

flex-wrap也存在响应式变体。

• .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

排序（Order）

使用一些order实用程序更改特定flex项的 visual 顺序。我们只提供第一个或最后一个项的选项，以及重置使用 DOM 顺序的选项。由于order采用 0 到 5 之间的任何整数值，因此请为所需的任何其他值添加自定义 CSS。

<div class="d-flex flex-nowrap">
  <div class="order-3 p-2">First flex item</div>
  <div class="order-2 p-2">Second flex item</div>
  <div class="order-1 p-2">Third flex item</div>
</div>

order也存在响应变体。

• .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

此外，还有响应式.order-first和.order-last类，它们分别通过应用order: -1和order: 6来更改元素的order。

• .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

对齐内容

在弹性框容器上使用align-content实用程序，在十字轴上将flex项_对齐_在一起_。从 start （浏览器默认）、end、 center、 between、 around 或stretch中进行选择。为了演示这些实用工具，我们强制执行了flex-wrap: wrap并增加了弹性商品的数量。

抬头！ 此属性对单行flex项没有影响。

<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>

align-content也存在响应式变体。

• .align-content-start
• .align-content-end
• .align-content-center
• .align-content-between
• .align-content-around
• .align-content-stretch
• .align-content-sm-start
• .align-content-sm-end
• .align-content-sm-center
• .align-content-sm-between
• .align-content-sm-around
• .align-content-sm-stretch
• .align-content-md-start
• .align-content-md-end
• .align-content-md-center
• .align-content-md-between
• .align-content-md-around
• .align-content-md-stretch
• .align-content-lg-start
• .align-content-lg-end
• .align-content-lg-center
• .align-content-lg-between
• .align-content-lg-around
• .align-content-lg-stretch
• .align-content-xl-start
• .align-content-xl-end
• .align-content-xl-center
• .align-content-xl-between
• .align-content-xl-around
• .align-content-xl-stretch
• .align-content-xxl-start
• .align-content-xxl-end
• .align-content-xxl-center
• .align-content-xxl-between
• .align-content-xxl-around
• .align-content-xxl-stretch

媒体对象

想要从 Bootstrap 4 复制 媒体对象组件？使用一些 flex 实用程序立即重新创建它，这些实用程序允许比以前更大的灵活性和自定义。

<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>

假设您想将内容垂直居中放在图像旁边：

<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>

Sass

实用程序 API

Flexbox 实用程序在我们的实用程序 API 中的 scss/_utilities.scss中声明。了解如何使用实用程序 API。

"flex": (
  responsive: true,
  property: flex,
  values: (fill: 1 1 auto)
),
"flex-direction": (
  responsive: true,
  property: flex-direction,
  class: flex,
  values: row column row-reverse column-reverse
),
"flex-grow": (
  responsive: true,
  property: flex-grow,
  class: flex,
  values: (
    grow-0: 0,
    grow-1: 1,
  )
),
"flex-shrink": (
  responsive: true,
  property: flex-shrink,
  class: flex,
  values: (
    shrink-0: 0,
    shrink-1: 1,
  )
),
"flex-wrap": (
  responsive: true,
  property: flex-wrap,
  class: flex,
  values: wrap nowrap wrap-reverse
),
"justify-content": (
  responsive: true,
  property: justify-content,
  values: (
    start: flex-start,
    end: flex-end,
    center: center,
    between: space-between,
    around: space-around,
    evenly: space-evenly,
  )
),
"align-items": (
  responsive: true,
  property: align-items,
  values: (
    start: flex-start,
    end: flex-end,
    center: center,
    baseline: baseline,
    stretch: stretch,
  )
),
"align-content": (
  responsive: true,
  property: align-content,
  values: (
    start: flex-start,
    end: flex-end,
    center: center,
    between: space-between,
    around: space-around,
    stretch: stretch,
  )
),
"align-self": (
  responsive: true,
  property: align-self,
  values: (
    auto: auto,
    start: flex-start,
    end: flex-end,
    center: center,
    baseline: baseline,
    stretch: stretch,
  )
),
"order": (
  responsive: true,
  property: order,
  values: (
    first: -1,
    0: 0,
    1: 1,
    2: 2,
    3: 3,
    4: 4,
    5: 5,
    last: 6,
  ),
),