.outer {
   display: flex;
   align-items: center; 
   justify-content: center;
 }

只使用Bootstrap类:

Div: class="容器d-flex" div中的元素:class="m-auto"

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.3/css/bootstrap.min.css" crossorigin="anonymous"> < span class=" font - family:宋体" style=" font - family:宋体;background - color: # 333;" > < h2 class = " m-auto " > < a href = " https://hovermind.com/ " > H➲版本➾M⇡ND < / > < / h2 > < / div >

使用CSS垂直居中，您可以让外部容器充当一个表，并将内容作为一个表单元格。在这种格式中，您的对象将保持居中。：）

我在JSFiddle中嵌套了多个对象作为一个例子，但核心思想是这样的:

HTML

<div class="circle">
  <div class="content">
    Some text
  </div>
</div>

CSS

.circle {
  /* Act as a table so we can center vertically its child */
  display: table;
  /* Set dimensions */
  height: 200px;
  width: 200px;
  /* Horizontal center text */
  text-align: center;
  /* Create a red circle */
  border-radius: 100%;
  background: red;
}

.content {
  /* Act as a table cell */
  display: table-cell;
  /* And now we can vertically center! */
  vertical-align: middle;
  /* Some basic markup */
  font-size: 30px;
  font-weight: bold;
  color: white;
}

多对象示例:

HTML

<div class="container">
  <div class="content">

    <div class="centerhoriz">

      <div class="circle">
        <div class="content">
          Some text
        </div><!-- content -->
      </div><!-- circle -->

      <div class="square">
        <div class="content">
          <div id="smallcircle"></div>
        </div><!-- content -->
      </div><!-- square -->

    </div><!-- center-horiz -->

  </div><!-- content -->
</div><!-- container -->

CSS

.container {
  display: table;
  height: 500px;
  width: 300px;
  text-align: center;
  background: lightblue;
}

.centerhoriz {
  display: inline-block;
}

.circle {
  display: table;
  height: 200px;
  width: 200px;
  text-align: center;
  background: red;
  border-radius: 100%;
  margin: 10px;
}

.square {
  display: table;
  height: 200px;
  width: 200px;
  text-align: center;
  background: blue;
  margin: 10px;
}

.content {
  display: table-cell;
  vertical-align: middle;
  font-size: 30px;
  font-weight: bold;
  color: white;
}

#smallcircle {
  display: inline-block;
  height: 50px;
  width: 50px;
  background: green;
  border-radius: 100%;
}

结果

https://jsfiddle.net/martjemeyer/ybs032uc/1/

哇，这个问题很受欢迎。这是基于对垂直对齐属性的误解。这篇优秀的文章解释了这一点:

理解垂直对齐，或者Gavin Kistner的“如何(不)垂直居中内容”。

“如何在CSS中居中”是一个很好的网络工具，它可以帮助您在不同的情况下找到必要的CSS居中属性。

简而言之(并防止链接腐烂):

Inline elements (and only inline elements) can be vertically aligned in their context via vertical-align: middle. However, the “context” isn’t the whole parent container height, it’s the height of the text line they’re in. jsfiddle example For block elements, vertical alignment is harder and strongly depends on the specific situation: If the inner element can have a fixed height, you can make its position absolute and specify its height, margin-top and top position. jsfiddle example If the centered element consists of a single line and its parent height is fixed you can simply set the container’s line-height to fill its height. This method is quite versatile in my experience. jsfiddle example … there are more such special cases.

我们可以使用CSS函数计算来计算元素的大小，然后相应地定位子元素。

示例HTML:

<div class="box">
    <span><a href="#">Some Text</a></span>
</div>

和CSS:

.box {
    display: block;
    background: #60D3E8;
    position: relative;
    width: 300px;
    height: 200px;
    text-align: center;
}

.box span {
    font: bold 20px/20px 'source code pro', sans-serif;
    position: absolute;
    left: 0;
    right: 0;
    top: calc(50% - 10px);
}

a {
    color: white;
    text-decoration: none;
}

演示创建在这里:https://jsfiddle.net/xnjq1t22/

这个解决方案工作良好的响应div高度和宽度以及。

注意:没有测试calc函数与旧浏览器的兼容性。

<div id="header" style="display: table-cell; vertical-align:middle;">

...

或CSS

.someClass
{
   display: table-cell;
   vertical-align:middle;
}

浏览器覆盖