message: fix(Step): fix z-index issue
diff: border-bottom-width: 1px;
  }
  - &:first-child {
  - &::before {
  - position: absolute;
  - top: 0;
  - left: -15px;
  - z-index: 1;
  - width: 1px;
  - height: 20px;
  - background-color: var(--van-white);
  - content: '';
  - }
  - }
  -
  .van-step__circle-container {
  position: absolute;
  top: 19px;
  left: -15px;
  - z-index: 2;
  + z-index: 1;
  font-size: var(--van-step-icon-size);
  line-height: 1;
  transform: translate(-50%, -50%);
  