align-items

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。

与align-content属性的区别在于它指定了当前Flex容器的行中的项目的对齐方式，而align-content则指定了行自身的对齐方式。

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>

var itemsAlignment = document.getElementById("itemsAlignment");
itemsAlignment.addEventListener("change", function (evt) {
  document.getElementById("container").style.alignItems = evt.target.value;
});

规范

浏览器兼容性

[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

• 使用CSS弹性框