CSS居中问题总结

1、居中元素宽高固定

• 绝对定位+margin

// top和left 为 50%， margin的left和top为自身宽高一半
.center {
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -height/2;
  margin-top: -width/2;
}

• 绝对定位+calc

.center {
  position: absolute;
  top: calc(50% - height/2);
  left: calc(50% - width/2);
}

2、被居中元素宽高不定

• transform变换

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

• flex+auto

.parent {
  display: flex;
}
.center {
  margin: auto;
}

• flex

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