.navbar {
  position: fixed;
  left: 0;
  top: 140px;
  width: 250px;
  height: 800px;
  background-color: #ffffff;
  z-index: 1000;
  box-shadow: none; /* 移除阴影效果 */
}

/* 响应式媒体查询 */
@media screen and (min-width: 769px) {
  .navbar {
    display: block;
  }
}

@media screen and (max-width: 768px) {
  .navbar {
    display: none;
  }
}