实现一个宽高自适应的正方形

.square {
  width: 10%;
  height: 10vw;
  background: tomato;
}

.square {
  width: 20%;
  height: 0;
  padding-top: 20%;
  background: orange;
}

.square {
  width: 30%;
  overflow: hidden;
  background: yellow;
}
.square::after {
  content: '';
  display: block;
  margin-top: 100%;
}