.sider_nav {
  background: #f4f4f6;
  .nav_btn {
    width: 28px;
    height: 28px;
    background-color: #fff;
    border-radius: 5px;
    cursor: pointer;
    color: #727b8d;
  }
  .sider_animation {
    position: fixed;
    top: 0;
    bottom: 0;
    width: 260px;
    height: 100%;
    left: 0;
    transition: all 200ms cubic-bezier(0.4, 0, 0.2, 1);
    overflow: hidden;
  }
}
