width与高之间自动适应

div {
          width: 100%;
          position: relative;
          &::after {
            content: '';
            display: block;
            padding-top: 100%;
            visibility: hidden;
          }
          img {
            position: absolute;
            top: 0;
            left: 0;
          }
        }
padding用百分比做单位时是相对于容器的宽度来算的