当两个div都有绝对位置时，在父div中居中

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

.child {
  position: absolute;
}

.parent {
  position: relative;
}

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

.parent {
  position: relative;
}

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