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概述

CSS align-items 属性以与justify-content相同的方式在侧轴方向上将当前行上的弹性元素对齐。

The difference to the align-content property is that it specifies the alignment of the items within the current flex container's line, whereas align-content specifies the alignment of the lines themselves.

初始值stretch
适用元素flex containers
是否是继承属性
适用媒体visual
计算值as specified
Animation typediscrete
正规顺序the unique non-ambiguous order defined by the formal grammar

语法

/* Basic keywords */
align-items: normal;
align-items: stretch;

/* Positional alignment */
align-items: center; /* Pack items around the center */
align-items: start; /* Pack items from the start */
align-items: end; /* Pack items from the end */
align-items: flex-start; /* Pack flex items from the start */
align-items: flex-end; /* Pack flex items from the end */
align-items: self-start;
align-items: self-end;
align-items: left; /* Pack items from the left */
align-items: right; /* Pack items from the right */

/* Baseline alignment */ justify-items: baseline;
align-items: first baseline;
align-items: last baseline; /* Overflow alignment (for positional alignment only) */
align-items: safe center;
align-items: unsafe center;

/* Global values */
align-items: inherit;
align-items: initial;
align-items: unset;

取值

normal
The effect of this keyword is dependent of the layout mode we are in:
  • In absolutely-positioned layouts, the keyword behaves like start on replaced absolutely-positioned boxes, and as stretch on all other absolutely-positioned boxes.
  • In static position of absolutely-positioned layouts, the keyword behaves as stretch.
  • For flex items, the keyword behaves as stretch.
  • For grid items, this keyword leads to a behavior similar to the one of stretch, except for boxes with an aspect ratio or an intrinsic sizes where it behaves like start.
  • The property doesn't apply to block-level boxes, and to table cells.
flex-start
元素向侧轴起点对齐。
flex-end
元素向侧轴终点对齐。
start
The item is packed flush to each other toward the start edge of the alignment container in the appropriate axis.
end
The item is packed flush to each other toward the end edge of the alignment container in the appropriate axis.
center
元素在侧轴居中。如果元素在侧轴上的高度高于其容器,那么在两个方向上溢出距离相同。
left
The items are packed flush to each other toward the left edge of the alignment container. If the property’s axis is not parallel with the inline axis, this value behaves like start.
right
The items are packed flush to each other toward the right edge of the alignment container in the appropriate axis. If the property’s axis is not parallel with the inline axis, this value behaves like start.
self-start
The items is packed flush to the edge of the alignment container of the start side of the item, in the appropriate axis.
self-end
The item is packed flush to the edge of the alignment container of the end side of the item, in the appropriate axis.
baseline
first baseline
last baseline
所有元素向基线对齐。侧轴起点到元素基线距离最大的元素将会于侧轴起点对齐以确定基线。
stretch
弹性元素被在侧轴方向被拉伸到与容器相同的高度或宽度。
safe
If the size of the item overflows the alignment container, the item is instead aligned as if the alignment mode were start.
unsafe
Regardless of the relative sizes of the item and alignment container, the given alignment value is honored.

语法格式

flex-start | flex-end | center | baseline | stretch

Example

CSS

#container {
  display: flex;
  height:200px;
  width: 240px;
  flex-wrap: wrap;
  align-items: flex-end; /* Can be changed in the live sample */
  background-color: #8c8c8c;
}

div > div {
  border: 2px solid #8c8c8c;
  width: 50px;
}

#item1 {
  background-color: #8cffa0;
  min-height: 30px;
}

#item2 {
  background-color: #a0c8ff;
  min-height: 50px;
}

#item3 {
  background-color: #ffa08c;
  min-height: 40px;
}

#item4 {
  background-color: #ffff8c;
  min-height: 60px;
}

#item5 {
  background-color: #ff8cff;
  min-height: 70px;
}

#item6 {
  background-color: #8cffff;
  min-height: 50px;
}

HTML

<div id="container">
  <div id="item1"></div>
  <div id="item2"></div>
  <div id="item3"></div>
  <div id="item4"></div>
  <div id="item5"></div>
  <div id="item6"></div>
</div>
<select id="itemsAlignment">
  <option value="flex-start">flex-start</option>
  <option value="flex-end" selected>flex-end</option>
  <option value="center">center</option>
  <option value="baseline">baseline</option>
  <option value="stretch">stretch</option>
</select>

规范

规范 状态 说明
CSS Box Alignment Module
align-items
Working Draft Adds the space-evenly, [ first | last ]? baseline, start, end, left, and right values.
CSS Flexible Box Layout Module
align-items
Candidate Recommendation Initial definition

浏览器兼容性

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 21.0-webkit[1] (Yes)-webkit
(Yes)
20.0 (20.0)[2] 11.0[3] 12.10 7.0-webkit
space-evenly, first/last baseline, start, end, left, right ? ? 45 (45) ? ? ?
Feature Android Android Webview Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support 4.4 (Yes) (Yes)-webkit
(Yes)
20.0 (20.0)[2] 未实现 12.10 7.0-webkit ?
space-evenly, first/last baseline, start, end, left, right ? ? ? 45.0 (45) ? ? ? ?

[1] Older versions of the spec treat absolute positioned children as though they are a 0 by 0 flex item. Later spec versions take them out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.

[2]用户需要访问about:config并将layout.css.flexbox.enabled设置为true以在Firefox 18和19中使用弹性框。从Firefox 28开始支持多行弹性框。 Multi-line flexbox has been supported since Firefox 28.

In addition to the unprefixed support, Gecko 48.0 (Firefox 48.0 / Thunderbird 48.0 / SeaMonkey 2.45) added support for a -webkit prefixed version of the property for web compatibility reasons behind the preference layout.css.prefixes.webkit, defaulting to false. Since Gecko 49.0 (Firefox 49.0 / Thunderbird 49.0 / SeaMonkey 2.46) the preference defaults to true.

[3] 在Internet Explorer 10到11中,如果列式弹性元素具备align-items属性并且其内容过大,那么会溢出容器而不会撑开。12以上没有这个问题。更多信息可以查看Flexbug #2

参考

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