Use:

# Parent
{
  display: table;
}

# Child
{
  display: table-cell;
  width: 100%; /* As large as its parent to center the text horizontally */
  text-align: center;
  vertical-align: middle; /* Vertically align this element on its parent */
}

<div class="small-container">
    <span>Text centered</span>
</div>

<style>
.small-container {
    width:250px;
    height:250px;
    border:1px green solid;
    text-align:center;
    position: absolute;
    top: 50%;
    left: 50%;
    -moz-transform: translateX(-50%) translateY(-50%);
    -webkit-transform: translateX(-50%) translateY(-50%);
    transform: translateX(-50%) translateY(-50%);
}
.small-container span{
    position: absolute;
    top: 50%;
    left: 50%;
    -moz-transform: translateX(-50%) translateY(-50%);
    -webkit-transform: translateX(-50%) translateY(-50%);
    transform: translateX(-50%) translateY(-50%);
}
</style>

这适用于我(测试OK!):

HTML:

<div class="mydiv">
    <p>Item to be centered!</p>
</div>

CSS:

.mydiv {
    height: 100%; /* Or other */
    position: relative;
}

.mydiv p {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%); /* To compensate own width and height */
}

您可以选择50%以外的其他值。例如，25%到父母的25%的中心。

使用flexbox / CSS:

<div class="box">
    <p>&#x0D05;</p>
</div>

CSS:

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

摘自《快速提示:垂直和水平居中元素的最简单方法》

在父div中添加以下代码

display: grid;
place-items: center;

我总是在容器中使用以下CSS，使其内容水平和垂直居中。

display: -webkit-box;
display: -moz-box;
display: -ms-flexbox;
display: -webkit-flex;
display: flex;

-webkit-box-align: center;
-moz-box-align: center;
-ms-flex-align: center;
-webkit-align-items: center;
align-items: center;

-webkit-box-pack: center;
-moz-box-pack: center;
-ms-flex-pack: center;
-webkit-justify-content: center;
justify-content: center;

在这里查看它的实际操作:https://jsfiddle.net/yp1gusn7/