.footer {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  min-height: 55px;
  box-shadow: 0px -1px 4px 0px rgba(0, 0, 0, 0.04);
  background: #ffffff;
  z-index: 100;
  box-sizing: border-box;
  padding-bottom: constant(safe-area-inset-bottom); /* 兼容iOS 11.0 - 11.2 */
  padding-bottom: env(safe-area-inset-bottom); /* 兼容iOS 11.2+ */
}