Flexbox CSS 的基础属性就是 display: flex ，只需要给元素添加这个属性，你就用上了弹性布局了。就这么简单！
你也许会问，这个属性起了什么作用？默认情况下，它指定了容器中的子元素沿主轴（main axis）排列，主轴默认是水平方向的。
接下来，我们会用两个实例来介绍这个属性是如何用在我们的 UI 组件的。
### 步进计数器 Demo
我们要介绍的第一个例子是步进输入框组件。当绑定 JavaScript 代码之后，点击 + / - 号，输入框中的值将会对应增加 / 减少。
译注：此处计数器的实现也可以使用 CSS Counters 来代替 JavaScript，具体例子可以参考 使用 CSS 的 counter-increment 做的游戏 。
按照以往的思路，你可能会选择用 display: inline-block 或者 float: left 来实现这种内联样式。然而，这样做的话，你还需要给这些元素统统添加特定的选择器。让我们使用弹性盒子吧，只需要往容器添加 display: flex 属性，就可以实现相同的效果了。
当你添加这个属性时，相当于对元素说：“嘿伙计，你就负责按照 flexbox 的规则排列你的子元素就好了！”。在最基本的形式下，元素沿主轴（main axis）排列，默认就是 x 轴，从左到右。
CSS 代码
```CSS
.stepperInput {
/**
* Setting display to flex makes this container lay
* out its children using flexbox. By default, it
* orders items horizontally, top-aligned.
* This has a similar effect to setting the children
* to have display: inline-block.
*/
display: flex;
}
.stepperInput__input {
border-left: 0;
border-right: 0;
width: 60px;
text-align: center;
}
.button {
cursor: pointer;
padding: 5px 15px;
color: #FFFFFF;
background-color: #4EBBE4;
font-size: 12px;
border: 1px solid #16A2D7;
border-radius: 4px;
}
.button–addOnLeft {
border-top-right-radius: 0;
border-bottom-right-radius: 0;
}
.button–addOnRight {
border-top-left-radius: 0;
border-bottom-left-radius: 0;
}
.input {
border: 1px solid #D7DBDD;
padding: 0 10px;
border-radius: 0;
box-shadow: none;
}
```
HTML 代码```HTML
### 标签页 [Demo](http://www.flexboxpatterns.com/tabs)同理，使用 `display: flex` 也可以实现这种标签页效果。CSS 代码```CSS.tabs { /** * Setting display to flex makes this container lay * out its children using flexbox, the exact same * as in the above "Stepper input" example. */ display: flex; border-bottom: 1px solid #D7DBDD;}.tab { cursor: pointer; padding: 5px 30px; color: #16A2D7; font-size: 12px; border-bottom: 2px solid transparent;}.tab.is-tab-selected { border-bottom-color: #4EBBE4;}
HTML 代码```HTML
Tab 1
Tab 2
Tab 3
Tab 4
_译注：tab 的切换效果可以通过纯 CSS 实现，可以参考 [CSS trick for tabs without javascript demo](http://poppinlp.com/demos/tabs-without-javascript.html)_### 站点头部 [Demo](http://www.flexboxpatterns.com/site-header)你可以把这种组件作为网站或者 webapp 的顶部。要构建这种组件，典型方法是把 logo 和导航按钮包裹在一个容器，设置按钮放在另一个容器中。然后，使用 `float` 把两个容器方别推向两边。紧接着，你要对整个顶部元素清除浮动。对于一个简单布局而言，这也太复杂了。如果使用弹性盒子，你依然需要容器元素，但是你不需要为容器添加特定的样式了，因为 flexbox 已经让父元素来负责布局了。除开 `display: flex` 属性外，我们还需要另外两个属性来调整布局：* `justify-content: space-between` 让容器左右分开成为了可能。这个属性把 logo 和导航按钮推向了左边，把设置推向了右边。* `align-items: center` 讲主轴上的元素垂直居中对齐。这个属性很重要，因为 logo 和导航按钮高度不同，如果不设置该属性，它们默认会对齐上边沿。```CSS.siteHeader { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Make the container put as much space as possible * between its children, with the children at either * end laying flush against the container's edges. */ justify-content: space-between; padding: 10px; background-color: #56727C;}.siteHeader__section { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * Align the children in the center, along * the main axis. By default the children will * align along their top edges. */ align-items: center;}.siteHeader__item { padding: 5px 15px; font-size: 12px;}.siteHeader__item + .siteHeader__item { margin-left: 5px;}.siteHeader__item.is-site-header-item-selected { color: #FFFFFF; background-color: #415F69; border-radius: 4px;}.siteHeaderLogo { font-size: 20px; line-height: 0; color: white;}.siteHeaderButton { cursor: pointer; color: #D9E9EF;}
InboxSentTrashSettings
### 表单底部 Demo
你也许需要在表单底部放个进度圈或者验证反馈。和上面的例子类似，使用弹性盒子可以将这些内容和表单提交按钮分隔开来。
CSS 代码
```CSS
.formFooter {
/**
* Lay out the children of this container with
* flexbox, which is horizontal by default.
*/
display: flex;
/**
* Align the children in the center, along
* the main axis, which is horizontal in this case.
*/
align-items: center;
/**
* Make the container put as much space as possible
* between its children, with the children at either
* end laying flush against the container’s edges.
*/
justify-content: space-between;
border-top: 1px solid #D7DBDD;
padding: 10px;
}
.formFooter__section {
/**
* This container orders items horizontally.
*/
display: flex;
/**
* It aligns them vertically in the center.
*/
align-items: center;
}
.formFooter__item + .formFooter__item {
margin-left: 5px;
}
.formFooterFeedback {
color: #86969C;
font-size: 12px;
line-height: 0;
}
.formFooterSpinner {
animation: formFooterSpinner 1s infinite steps(8, end);
}
@keyframes formFooterSpinner {
0% { transform: rotate(0deg); }
100% { transform: rotate(360deg); }
}
.button–clear {
color: #16A2D7;
background-color: #FFFFFF;
border: 1px solid #FFFFFF;
}
```
HTML 代码```HTML
Saving...
Reset
Save
### 侧边栏 [Demo](http://www.flexboxpatterns.com/side-bar)这也是一个相当经典的组件。你甚至不需要 flexbox 来构造它，div 就足够了…… 不过，如果设计师让你把其中一个按钮单独拿到下面，你可以用 `position: absolute` 来处理，当然也可以用 flexbox。除了 `display: flex` 和 `justify-content: space-between`，我们还需要另一个属性：* `flex-direction: column` 会将主轴 (main axis) 从水平方向改为垂直方向。正如你所猜测的那样，现在子元素将会垂直排列了。CSS 代码```CSS.sideBar { /** * This container orders items according to flexbox * rules. By default, this would arrange its children * horizontally. However, the next property... */ display: flex; /** * ...sets the main axis to be vertical instead of * horizontal, so now the children are laid out * vertically, from top to bottom. */ flex-direction: column; /** * It will also put as much space as possible * between its children, with the children at either end * laying flush against the container's edges. */ justify-content: space-between; height: 300px; width: 150px; border-right: 1px solid #D7DBDD; background-color: #FCFDFD; padding: 10px;}.sideBar__item { cursor: pointer; padding: 5px 10px; color: #16A2D7; font-size: 12px;}.sideBar__item.is-side-bar-item-selected { background-color: #EEF3F5; border-radius: 4px;}
HTML 代码```HTML
Inbox
Contacts
Account
Legal
### 居中提示 [Demo](http://www.flexboxpatterns.com/centered-prompt)不使用 flexbox 的居中布局通常需要一些 hack 技巧，比如使用绝对布局然后通过 2D transform 平移。使用 flexbox，你只需要在容器元素设置 4 个属性：* `display: flex`* `flex-direction: column`* `align-items: center` 设置或检索弹性盒子元素在侧轴（纵轴）方向上的对齐方式。在这里和设置 `text-align: center` 的效果有点类似。* `justify-content: center` 子元素向主轴中心紧挨靠拢。CSS 代码```CSS.centeredPrompt { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * Rotate the main axis so that the children * are laid out vertically, the same as in the * above "Side bar" example. */ flex-direction: column; /** * Align the children in the center, along * the main axis. Because the direction is * "column" this has a similar effect as setting * text-align: center. */ align-items: center; /** * Instead of pushing the children apart, as in * previous examples, we will group them together * in the center of their container. */ justify-content: center; min-height: 300px; padding: 10px;}.centeredPrompt__item + .centeredPrompt__item { margin-top: 5px;}.centeredPromptIcon { font-size: 60px; line-height: 0;}.centeredPromptLabel { color: #86969C; font-size: 30px; font-weight: 700; text-align: center;}.centeredPromptDetails { color: #86969C; font-size: 16px; margin-bottom: 10px; text-align: center;}.icon { color: #BCD2DA;}
HTML 代码```HTML
Welcome to the app!
Thanks for signing up. Let’s take a look around.
Begin tour
### 居中图标 [Demo](http://www.flexboxpatterns.com/centered-icon)使用同样的方法，我们还可以居中更多东西，比如图标。CSS 代码```CSS.centeredIcon { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * As in the above "Centered prmopt" example, * we'll rotate the main axis so that the children * are ordered vertically. */ flex-direction: column; /** * And just like in that example, align the children * in the center, along the main axis. */ align-items: center; /** * Same thing here as before: group the children * together in the center of their container. */ justify-content: center; border: 1px solid #D7DBDD; font-size: 40px; width: 90px; height: 90px; border-radius: 100%; box-shadow: 0 2px 1px rgba(0, 0, 0, 0.05), 0 2px 3px rgba(0, 0, 0, 0.05), 0 4px 8px rgba(0, 0, 0, 0.05);}
HTML 代码```HTML
### 功能列表 [Demo](http://www.flexboxpatterns.com/feature-list)在这个列表中，其中一行是反向排列的，实现方法很简单，只需要添加一个 flexbox 属性：`flex-direction: row-reverse` 把容器中的子元素按照 HTML 中的顺序反向排列。CSS 代码```CSS.featureListItem { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Align the children in the center, along * the main axis, which is horizontal in this case. */ align-items: center; max-width: 400px; padding: 10px;}.featureListItem + .featureListItem { border-top: 1px solid #D7DBDD;}.featureListItem--reverse { /** * We can specify the flex-direction so that * the children elements are displayed in the * reverse order of how they appear in the * markup. */ flex-direction: row-reverse;}.featureListItem__icon,.featureListItem__description { padding: 5px 15px;}.featureListItem__icon { font-size: 50px; line-height: 0;}.featureListItem__description { color: #86969C; font-size: 12px;}
HTML 代码```HTML
The calendar feature makes scheduling a snap.
Our dashboard gives you a bird’s-eye-view-at-a-glance-on-the-go.
You can get notified by email or SMS.
### 卡片 [Demo](http://www.flexboxpatterns.com/card)接下来复习一下，这个卡片的组件用到了此前提到的属性。* display: flex* flex-direction: column* align-items: center* justify-content: center这里没什么新的知识点，但是为我们接下来要介绍的卡片组做了铺垫。CSS 代码```CSS.card { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Rotate the main axis so that the children * are laid out vertically. */ flex-direction: column; border: 1px solid #CAD0D2; border-radius: 4px; overflow: hidden;}.card__description { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * We're going to lay out this element's children * just like in the "Centered prompt" example. * First we'll rotate the main axis so that the * children are laid out vertically. */ flex-direction: column; /** * Just like in the "Centered prompt" example, * we'll align the children in the center, along * the main axis. */ align-items: center; /** * And just like in the "Centered prompt", we'll * group the children in the center of their * container. */ justify-content: center; padding: 15px;}.card__descriptionIcon { font-size: 32px; margin-bottom: 10px;}.card__descriptionText { color: #57727C; font-size: 12px; text-align: center;}.card__price { text-align: center; color: #57727C; font-size: 12px; font-weight: 700; padding: 5px 15px; border-top: 1px solid #D7DBDD; background-color: #EEF3F5;}.card--fixedWidth { max-width: 120px;}
HTML 代码```HTML
Science potion
Costs $5
### 卡片组 [Demo](http://www.flexboxpatterns.com/card-group)现在我们来学习最后一个 “卡片组” 组件。我们需要考虑两个麻烦的地方：1. 我们想要每个卡片的宽度相等，但是里面包含的内容多少可能各不相同。2. 我们想要所有的卡片注释高度相等，同样，每张卡片的注释长度也不相等。不适用 flexbox，你可能会想到使用 `table` 元素来实现这些需求，或者对所有元素使用绝对布局，并组合使用百分比、像素和 calc() 来实现。这样也太复杂了。使用弹性盒子，整个问题的解决方案就变得优雅多了。这里我们引入一个新的属性，但是和之前我们提到的属性不同，这个属性应用在 **子元素** 而不是容器。我们为每张卡片设置 `flex: 1 1 0`，使得每张卡片的宽度相等。这个属性是以下三个属性的简写方法：* `flex-grow: 1` 设置或检索弹性盒的扩展比率。默认值为 0，我们设置为 1，此时卡片会尽可能扩展以填充容器。* `flex-shrink: 1` 设置或检索弹性盒的收缩比率。默认值为 1。我们设置为 1，此时卡片会尽可能收缩以适应容器。* `flex-basis: 0` 设置或检索弹性盒伸缩基准值。设置为 0 的时候，其大小仅由容器的大小所决定。这些属性满足了第一点要求。对于我们的第二个要求，我们可以对 flex 属性稍作调整，改成 `flex: 1 1 auto`。* `flex-basis: auto` 导致卡片注释的高度自适应，意思就是最长的注释框拥有最大的高度。由于注释同时拥有 `flex-grow: 1` 属性，因此较短注释的卡片会自动伸长来适配容器高度。CSS 代码```CSS.cardGroup { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; border: 1px solid #CAD0D2; border-radius: 4px; overflow: hidden;}.cardGroup__card { /** * The flex property is a short-hand for setting * the flex-shrink, flex-grow, and flex-basis * properties. These properties control how the * element resizes to fill its container. * * We'll also set flex-grow to 1 so that it * will expand to fill its container. (The * default value is 0.) * * We'll set flex-shrink to 1 so that the element * will shrink as its container gets smaller. * (The default value is 1.) * * Last, we set flex-basis to 0 so that its * size is solely determined by the size of * the container. (The default value * is auto, which would cause the content's * size to also be a factor in this calculation.) * * The net result of these properties is that the * element is a fluid size, and will expand and * shrink with its container and siblings, but * they will all have the same size, even if they * have different amounts of content. */ flex: 1 1 0; border: none; border-radius: 0;}.cardGroup__card + .cardGroup__card { border-left: 1px solid #D7DBDD;}.cardGroup__cardDescription { /** * We're doing almost the exact same thing here as * we did above. The difference is that its * flex-basis is auto, so now the size of its content * will affect how large it is. */ flex: 1 1 auto;}
HTML 代码```HTML
Trial
Free!
Basic tier(most popular)
$10.00
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$6,000.00
```