.site-header {
    position: fixed;
    top: 0;
    right: 0;
    left: 0;
    z-index: 99;
    height: 64px;
    border-bottom: 1px solid var(--border);
    background: rgba(255, 255, 255, .95);
    backdrop-filter: blur(20px);
    transition: background-color .2s ease;
}

.site-header-inner {
    display: flex;
    align-items: center;
    gap: 40px;
    height: 100%;
    padding: 0 var(--page-gutter);
}

.site-logo {
    display: flex;
    flex-shrink: 0;
    align-items: center;
}

.site-logo img {
    width: auto;
    height: 42px;
    object-fit: contain;
}

.site-nav {
    display: flex;
    flex: 1;
    align-items: center;
    gap: 28px;
}

.site-nav a {
    position: relative;
    color: var(--text-2);
    font-size: .88rem;
    font-weight: 600;
    padding-block: 22px;
    transition: color .15s ease;
}

.site-nav a:hover {
    color: var(--green);
}

.site-nav a::after {
    position: absolute;
    right: 0;
    bottom: 0;
    left: 0;
    width: 0;
    height: 3px;
    margin: auto;
    border-radius: 3px 3px 0 0;
    background: var(--green);
    content: "";
    transition: width .2s ease;
}

.site-nav a.is-active {
    color: var(--green-dark);
}

.site-nav a.is-active::after {
    width: 100%;
}

/* Dropdown "Tài liệu" */
.site-nav-drop {
    position: relative;
}

.site-nav-drop > button {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    padding: 22px 0;
    border: 0;
    background: none;
    color: var(--text-2);
    font: inherit;
    font-size: .88rem;
    font-weight: 600;
    cursor: pointer;
}

.site-nav-drop > button .lucide {
    transform: rotate(90deg);
    transition: transform .15s ease;
}

.site-nav-drop:hover > button,
.site-nav-drop:focus-within > button {
    color: var(--green);
}

.site-nav-drop:hover > button .lucide,
.site-nav-drop:focus-within > button .lucide {
    transform: rotate(-90deg);
}

.site-nav-menu {
    position: absolute;
    top: 100%;
    left: -16px;
    display: flex;
    flex-direction: column;
    width: 280px;
    padding: 8px;
    border: 1px solid var(--border);
    border-radius: 16px;
    background: var(--white);
    visibility: hidden;
    opacity: 0;
    transform: translateY(-6px);
    transition: opacity .15s ease, transform .15s ease, visibility .15s;
}

.site-nav-drop:hover .site-nav-menu,
.site-nav-drop:focus-within .site-nav-menu {
    visibility: visible;
    opacity: 1;
    transform: translateY(0);
}

.site-nav .site-nav-menu a {
    display: flex;
    flex-direction: column;
    gap: 2px;
    padding: 10px 12px;
    border-radius: 10px;
}

.site-nav .site-nav-menu a::after {
    display: none;
}

.site-nav .site-nav-menu a:hover {
    background: var(--green-pale);
}

.site-nav-menu b {
    color: var(--text);
    font-size: .9rem;
}

.site-nav-menu small {
    color: var(--text-2);
    font-size: .78rem;
    font-weight: 500;
}

.site-header-actions {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-left: auto;
}

.header-button {
    border-radius: 12px;
    font-size: .85rem;
    font-weight: 700;
    transition: color .2s ease, border-color .2s ease, background-color .2s ease, transform .15s ease;
}

.header-button-ghost {
    padding: 8px 20px;
    border: 2px solid var(--border);
    background: transparent;
    color: var(--text);
}

.header-button-ghost:hover {
    border-color: var(--green);
    color: var(--green);
}

.header-button-primary {
    padding: 9px 22px;
    border-bottom: 3px solid var(--green-dark);
    background: var(--green);
    color: var(--white);
    letter-spacing: .2px;
}

.header-button-primary:hover {
    background: #4eb802;
    transform: translateY(-1px);
}

@media (max-width: 1000px) {
    .site-header-inner {
        gap: 24px;
    }

    .site-nav {
        gap: 18px;
    }

    .site-nav a:nth-last-child(-n + 2) {
        display: none;
    }
}

.menu-toggle {
    display: none;
    flex-direction: column;
    justify-content: center;
    gap: 4px;
    width: 40px;
    height: 40px;
    padding: 0 10px;
    border: 0;
    border-radius: 10px;
    background: var(--surface);
    cursor: pointer;
}

.menu-toggle span {
    display: block;
    height: 2px;
    border-radius: 2px;
    background: var(--text);
    transition: transform .2s ease, opacity .2s ease;
}

.menu-toggle.is-open span:nth-child(1) {
    transform: translateY(6px) rotate(45deg);
}

.menu-toggle.is-open span:nth-child(2) {
    opacity: 0;
}

.menu-toggle.is-open span:nth-child(3) {
    transform: translateY(-6px) rotate(-45deg);
}

.mobile-menu {
    display: none;
}

@media (max-width: 800px) {
    .site-nav,
    .header-button-ghost {
        display: none;
    }

    .menu-toggle {
        display: flex;
    }

    .mobile-menu {
        position: absolute;
        top: 64px;
        right: 0;
        left: 0;
        display: flex;
        flex-direction: column;
        padding: 8px 16px 16px;
        border-bottom: 1px solid var(--border);
        background: var(--white);
        visibility: hidden;
        opacity: 0;
        transform: translateY(-8px);
        transition: opacity .2s ease, transform .2s ease, visibility .2s;
    }

    .mobile-menu.is-open {
        visibility: visible;
        opacity: 1;
        transform: translateY(0);
    }

    .mobile-menu a {
        padding: 12px 4px;
        border-bottom: 1px solid var(--border);
        color: var(--text);
        font-weight: 600;
    }

    .mobile-menu a:last-child {
        border-bottom: 0;
        color: var(--green-dark);
    }
}

@media (max-width: 640px) {
    .site-header-inner {
        gap: 0;
        padding: 0 16px;
    }

    .site-logo img {
        height: 36px;
    }

    .header-button-primary {
        padding-inline: 14px;
    }
}