.footer {
  height: 60px;
  background-color: #333;
  color: white;
  text-align: center;
  line-height: 60px;
  font-size: 14px;
}

.tapper {
  display: flex;
  flex-direction: column;
  min-height: 100vh; /* 保证总高度至少一屏 */
}