css-实现垂直水平居中

要求让一个 div 垂直水平居中

方法一：flex 布局

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

方法二：position 定位

1. div 宽高已知

div.parent {
  position: relative;
}
div.child {
  width: 50px;
  height: 10px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -25px;
  margin-top: -5px;
}
/* 或 */
div.child {
  width: 50px;
  height: 10px;
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  margin: auto;
}

2. div 宽高未知

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

方法三：grid 布局

div.parent {
  display: grid;
}
div.child {
  justify-self: center;
  align-self: center;
}

方法四：table 布局

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

方法五：inline-block

div.parent {
  font-size: 0;
  text-align: center;
  &::before {
    content: "";
    display: inline-block;
    width: 0;
    height: 100%;
    vertical-align: middle;
  }
}
div.child {
  display: inline-block;
  vertical-align: middle;
}