CSS各种居中解决方案

以下解决方案都为不定宽和高的情况下，结构如下：

<div class="parent">
  <div class="child"></div>
</div>

水平居中的解决方案

inline-block + text-align

.parent{
  text-align: center;
}
.child{
  display: inline-block;
}

table + margin

.child{
  display: table;
  margin: 0 auto;
}

absolute + transform

.parent{
  position: relative;
}
.child{
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
}

flex + justify-content

.parent{
  display: flex;
  justify-content: center;
}
或
.parent{
  display: flex;
}
.child{
  margin: 0 auto;
}

垂直居中的解决方案

table-cell + vertical-align

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

absolute + transform

.parent{
  position: relative;
}
.child{
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

flex + align-items

.parent{
  display: flex;
  align-items: center;
}

水平垂直居中

inline-block + text-align + table-cell + vertical-align

.parent{
  text-align: center;
  display: table-cell;
  vertical-align: middle;
}
.child{
  display: inline-block;
}

absolute + transform

.parent{
  position: relative;
}
.child{
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

flex + justify-content + align-items

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