html如何水平居中元素

如何使用 CSS 将一个

水平居中放置在另一个
中?

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

You can apply this CSS to the inner <div>:

#inner {
  width: 50%;
  margin: 0 auto;
}

Of course, you don't have to set the width to 50%. Any width less than the containing <div> will work. The margin: 0 auto is what does the actual centering.

If you are targeting Internet Explorer 8 (and later), it might be better to have this instead:

#inner {
  display: table;
  margin: 0 auto;
}

It will make the inner element center horizontally and it works without setting a specific width.

Working example here:

#inner {
  display: table;
  margin: 0 auto;
  border: 1px solid black;
}

#outer {
border: 1px solid red;
width:100%
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

EDIT

With flexbox it is very easy to style the div horizontally and vertically centered.

#inner {  
  border: 1px solid black;
}

#outer {
border: 1px solid red;
width:100%;
display: flex;
justify-content: center;
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

To align the div vertically centered, use the property align-items: center.

If you don't want to set a fixed width on the inner div you could do something like this:

#outer {
  width: 100%;
  text-align: center;
}

#inner {
display: inline-block;
}

<div id="outer">  
    <div id="inner">Foo foo</div>
</div>

That makes the inner div into an inline element that can be centered with text-align.

The best approaches are with CSS 3.

Box model:

#outer {
  width: 100%;
  /* Firefox */
  display: -moz-box;
  -moz-box-pack: center;
  -moz-box-align: center;
  /* Safari and Chrome */
  display: -webkit-box;
  -webkit-box-pack: center;
  -webkit-box-align: center;
  /* W3C */
  display: box;
  box-pack: center;
  box-align: center;
}

#inner {
width: 50%;
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

According to your usability you may also use the box-orient, box-flex, box-direction properties.

Flex:

#outer {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: center;
    align-items: center;
}

Read more about centering the child elements

And this explains why the box model is the best approach:

Suppose that your div is 200 pixels wide:

.centered {
  position: absolute;
  left: 50%;
  margin-left: -100px;
}

Make sure the parent element is positioned, i.e., relative, fixed, absolute, or sticky.

If you don't know the width of your div, you can use transform:translateX(-50%); instead of the negative margin.

https://jsfiddle.net/gjvfxxdj/

With CSS calc(), the code can get even simpler:


.centered {
  width: 200px;
  position: absolute;
  left: calc(50% - 100px);
}

The principle is still the same; put the item in the middle and compensate for the width.

Centering a div of unknown height and width

Horizontally and vertically. It works with reasonably modern browsers (Firefox, Safari/WebKit, Chrome, Internet & Explorer & 10, Opera, etc.)

.content {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}
<div class="content">This works with any content</div>

Tinker with it further on Codepen or on JSBin.

Set the width and set margin-left and margin-right to auto. That's for horizontal only, though. If you want both ways, you'd just do it both ways. Don't be afraid to experiment; it's not like you'll break anything.

It cannot be centered if you don't give it a width. Otherwise, it will take, by default, the whole horizontal space.

For Firefox and Chrome:

<div style="width:100%;">
  <div style="width: 50%; margin: 0px auto;">Text</div>
</div>

For Internet Explorer, Firefox, and Chrome:

<div style="width:100%; text-align:center;">
  <div style="width: 50%; margin: 0px auto; text-align:left;">Text</div>
</div>

The text-align: property is optional for modern browsers, but it is necessary in Internet Explorer Quirks Mode for legacy browsers support.

Use:

#outerDiv {
  width: 500px;
}

#innerDiv {
width: 200px;
margin: 0 auto;
}

<div id="outerDiv">
  <div id="innerDiv">Inner Content</div>
</div>
</div>