:root {
    --vn-red: #da251d; /* Màu đỏ cờ Việt Nam */
    --vn-yellow: #ffff00; /* Màu vàng ngôi sao */
    --vn-dark-red: #a81c16;
    --bg-light: #f8f9fa;
}

body {
    font-family: 'Inter', sans-serif;
    background-color: #f0f2f5;
    color: #1c1e21;
}

/* Navbar tông Đỏ - Vàng */
.navbar {
    background: var(--vn-red);
    box-shadow: 0 2px 10px rgba(0,0,0,0.2);
    z-index: 1080;
    height: 65px;
}
.navbar-brand {
    color: var(--vn-yellow) !important;
    display: flex;
    align-items: center;
    gap: 10px;
}
.navbar-brand i {
    color: var(--vn-yellow);
    font-size: 1.8rem;
}

/* Nút Tạo nhóm màu Vàng chữ Đỏ */
.btn-vn-yellow {
    background-color: var(--vn-yellow);
    color: var(--vn-red);
    border: none;
    font-weight: 700;
    transition: all 0.3s;
}
.btn-vn-yellow:hover {
    background-color: #e6e600;
    transform: translateY(-2px);
    color: var(--vn-dark-red);
}

/* Sidebar & Menu */
.nav-link-custom {
    display: flex;
    align-items: center;
    padding: 10px 15px;
    border-radius: 12px;
    color: #444;
    text-decoration: none;
    font-weight: 600;
    transition: all 0.2s ease;
    margin-bottom: 5px;
}
.nav-link-custom:hover {
    background: rgba(218, 37, 29, 0.1);
    color: var(--vn-red);
}
.nav-link-custom.active {
    background: var(--vn-red);
    color: white !important;
}
.nav-link-custom.active i {
    color: var(--vn-yellow) !important;
}
.nav-link-custom i {
    width: 35px;
    font-size: 1.2rem;
    color: var(--vn-red);
}

/* Card & Feed */
.fb-card {
    background: white;
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.05);
    margin-bottom: 20px;
    border: 1px solid rgba(0,0,0,0.05);
    overflow: hidden;
}
.btn-join {
    background: var(--vn-red);
    color: white;
    border-radius: 8px;
    border: none;
    padding: 6px 0;
    font-weight: 600;
}
.btn-join:hover {
    background: var(--vn-dark-red);
    color: var(--vn-yellow);
}

/* Mobile Menu Button */
.btn-menu-mobile {
    border: none;
    background: rgba(255, 255, 255, 0.2);
    color: white;
    border-radius: 8px;
    width: 40px;
    height: 40px;
}

.sticky-sidebar {
    position: sticky;
    top: 85px;
    height: calc(100vh - 100px);
    overflow-y: auto;
}

@media (max-width: 991.98px) {
    .sidebar-col {
        display: none;
    }
}


 


/* Container ảnh bài viết */
.post-images-grid {
    display: grid;
    gap: 2px;
    background-color: #fff;
    overflow: hidden;
    cursor: pointer;
}

.post-img-item {
    width: 100%;
    height: 100%;
    object-fit: cover;
    min-height: 200px;
}

/* Các trường hợp cụ thể */
.grid-1 { grid-template-columns: 1fr; }
.grid-1 .post-img-item { max-height: 500px; }

.grid-2 { grid-template-columns: 1fr 1fr; height: 300px; }

.grid-3 { grid-template-columns: 1fr 1fr; grid-template-rows: 200px 200px; }
.grid-3 .post-img-item:first-child { grid-row: span 2; }

.grid-4 { grid-template-columns: 1fr 1fr; grid-template-rows: 200px 200px; }

.grid-more { grid-template-columns: 1fr 1fr 1fr; grid-template-rows: 250px 150px; }
.grid-more .post-img-item:first-child { grid-column: span 3; }

/* Lớp phủ khi có > 4 ảnh */
.more-images {
    position: relative;
}
.more-overlay {
    position: absolute;
    top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.5);
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    font-weight: bold;
}