/* 二级菜单容器样式 */
.nav_item .second {
    transform: translateX(-50%) translateY(-10px);
    max-height: 0;
    overflow: hidden;
    /* 添加过渡效果，使动画平滑 */
    transition: all .3s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

/* 鼠标悬停时显示二级菜单并应用动画 */
.nav_item:hover .second {
    /* 最终状态 - 完全显示且位置正确 */
    visibility: visible;
    opacity: 1;
    transform: translateX(-50%) translateY(0);
    max-height: 500px; /* 足够大的值以容纳所有菜单项 */
}

/* 为每个二级菜单项添加依次出现的动画 */
.nav_item .second_item {
    /* 初始状态 - 透明且上移 */
    opacity: 0;
    transform: translateY(-10px);
}

/* 鼠标悬停时，为每个二级菜单项设置不同的延迟出现时间 */
.nav_item:hover .second_item:nth-child(1) { transition-delay: 0.1s; opacity: 1; transform: translateY(0); }
.nav_item:hover .second_item:nth-child(2) { transition-delay: 0.15s; opacity: 1; transform: translateY(0); }
.nav_item:hover .second_item:nth-child(3) { transition-delay: 0.2s; opacity: 1; transform: translateY(0); }
.nav_item:hover .second_item:nth-child(4) { transition-delay: 0.25s; opacity: 1; transform: translateY(0); }
.nav_item:hover .second_item:nth-child(5) { transition-delay: 0.3s; opacity: 1; transform: translateY(0); }