用CSS实现元素垂直居中

1.tabel 自带垂直居中

  <table class="parent">
    <tr>
      <td class="child">
      一串文字
      </td>
    </tr>
  </table>
  
.parent{
  border: 1px solid red;
  height: 600px;
}
.child{
  border: 1px solid green;
}

2.使用 span 占位，加上把 div 变成 inline block

<div class="parent">
  <span class=before></span><div class="child">
    一串文字
  </div><span class=after></span>
</div>

.parent{
  border: 1px solid red;
  height: 600px;
  text-align: center;
}
.child{
  border: 1px solid black;
  display: inline-block;
  width: 300px;
  vertical-align: middle;
}
.parent .before{
  outline: 1px solid red;
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}
.parent .after{
  outline: 1px solid red;
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}

3.使用伪元素

<div class="parent">
  <div class="child">
      一串文字
  </div>
</div>

.parent{
  border: 3px solid red;
  height: 600px;
  text-align: center;
}
.child{
  border: 3px solid black;
  display: inline-block;
  width: 300px;
  vertical-align: middle;
}
.parent:before{
  content:'';
  outline: 3px solid red;
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}
.parent:after{
  content:'';
  outline: 3px solid red;
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}

4.把 div 装成 tabel

<div class="table">
  <div class="td">
    <div class="child">
      一串文字
    </div>
  </div>
</div>

div.table{
  display: table;
  border: 1px solid red;
  height: 600px;
}
div.tr{
  display: table-row;
  border: 1px solid green;
}
div.td{
  display: table-cell;
  border: 1px solid blue;
  vertical-align: middle;
}
.child{
  border: 10px solid black;
}

5.使用 负 margin

<div class="parent">
  <div class="child">
    一串文字
  </div>
</div>

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  width: 300px;
  height: 100px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -150px;
  margin-top: -50px;
}

6.使用 transform 动画

<div class="parent">
  <div class="child">
    一串文字
  </div>
</div>

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
}

7.使用 margin auto

<div class="parent">
  <div class="child">
    一串文字
  </div>
</div>

.parent{
  height: 600px;
  border: 1px solid red;
  position: relative;
}
.child{
  border: 1px solid green;
  position: absolute;
  width: 300px;
  height: 200px;
  margin: auto;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}

8.使用 flex 布局

<div class="parent">
  <div class="child">
    一串文字
  </div>
</div>

.parent{
  height: 600px;
  border: 3px solid red;
  display: flex;
  justify-content: center;
  align-items: center;
}
.child{
  border: 3px solid green;
  width: 300px;
}