/* ===========================
   Navigation Styles
   =========================== */
header {
    background-color: var(--primary-color, #67A3B3);
    color: white;
    padding: 0;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1rem clamp(0.75rem, 3vw, 3rem);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo-section {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.logo-section img {
    height: 50px;
    width: auto;
}

.site-title-link {
    text-decoration: none;
    color: inherit;
}

.site-title-link:hover {
    opacity: 0.9;
}

.site-title {
    font-size: 2.1rem;
    margin: 0;
    color: #fff;
    font-weight: 800;
}

/* ===========================
   Navigation Menu
   =========================== */
nav ul {
    display: flex;
    list-style: none;
    gap: 2rem;
    margin: 0;
    padding: 0;
}

nav li {
    position: relative;
}

nav a {
    color: white;
    text-decoration: none;
    padding: 0.5rem 1rem;
    display: block;
    transition: all 0.3s ease;
    border-radius: 4px;
}

nav a:hover,
nav a.active {
    background-color: rgba(255, 255, 255, 0.1);
    color: var(--light-bg, #f7fbfc);
}

/* ===========================
   Dropdown Menus
   =========================== */
nav ul ul {
    position: absolute;
    top: 100%;
    left: 0;
    min-width: 220px;
    background: var(--white, #ffffff);
    border: 1px solid var(--border-color, #d9e7ec);
    border-radius: 10px;
    padding: 0.2rem 0;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.12);
    display: none;
    flex-direction: column;
    gap: 0;
    z-index: 1000;
}

nav ul ul li {
    width: 100%;
}

nav ul ul a {
    color: var(--secondary-color, #0b5565);
    padding: 0.3rem 0.85rem;
    border-radius: 0;
    line-height: 1.15;
    white-space: nowrap;
}

nav ul ul a:hover,
nav ul ul a.active {
    background-color: var(--light-bg, #f7fbfc);
    color: var(--secondary-color, #0b5565);
}

nav li:hover > ul,
nav li:focus-within > ul {
    display: flex;
}

nav ul ul ul {
    top: 0;
    left: 100%;
}

nav ul ul.submenu-left {
    left: auto;
    right: 100%;
}

nav li.has-submenu > a::after {
    content: "▾";
    font-size: 0.95rem;
    margin-left: 8px;
    font-weight: 700;
    opacity: 0.9;
}

nav ul ul li.has-submenu > a::after {
    content: "▾";
    display: inline-block;
    margin-left: 8px;
    font-size: 0.95rem;
    font-weight: 700;
    opacity: 0.9;
}

/* ===========================
   Mobile Menu Toggle
   =========================== */
.menu-toggle {
    display: none;
    flex-direction: column;
    cursor: pointer;
    padding: 0.5rem;
}

.menu-toggle span {
    width: 25px;
    height: 3px;
    background-color: white;
    margin: 3px 0;
    transition: 0.3s;
    border-radius: 2px;
}

/* ===========================
   Mobile Responsive
   =========================== */
@media (max-width: 768px) {
    .header-content {
        flex-wrap: wrap;
    }
    
    .menu-toggle {
        display: flex;
        order: 3;
    }
    
    nav {
        order: 4;
        width: 100%;
        max-height: 0;
        overflow: hidden;
        transition: max-height 0.3s ease;
    }
    
    nav.active {
        max-height: 500px;
    }
    
    nav ul {
        flex-direction: column;
        gap: 0;
        padding: 1rem 0;
    }
    
    nav a {
        padding: 1rem;
    }

    nav ul ul {
        position: static;
        min-width: auto;
        background: transparent;
        border: none;
        box-shadow: none;
        padding: 0;
        display: none; /* Hidden by default on mobile */
    }
    
    nav ul ul.mobile-open {
        display: block;
    }

    nav ul ul a {
        color: white;
        padding-left: 2.25rem;
    }

    nav ul ul ul a {
        padding-left: 3.25rem;
    }

    nav li.has-submenu > a::after,
    nav ul ul li.has-submenu > a::after {
        content: "▸";
        float: right;
        font-size: 0.95rem;
        font-weight: 700;
        opacity: 0.9;
        transition: transform 0.3s ease;
    }
    
    nav li.has-submenu.mobile-open > a::after,
    nav ul ul li.has-submenu.mobile-open > a::after {
        content: "▾";
    }
    
    /* Hamburger Animation */
    .menu-toggle.active span:nth-child(1) {
        transform: rotate(-45deg) translate(-5px, 6px);
    }
    
    .menu-toggle.active span:nth-child(2) {
        opacity: 0;
    }
    
    .menu-toggle.active span:nth-child(3) {
        transform: rotate(45deg) translate(-5px, -6px);
    }
}

/* Mobile-specific optimizations */
@media (max-width: 480px) {
    .header-content {
        padding: 0.75rem 0.5rem;
    }
    
    .site-title {
        font-size: 1.5rem;
    }
    
    .logo-section {
        gap: 0.5rem;
    }
    
    .logo-section img {
        height: 40px;
    }
}

/* ===========================
   Chapter Navigation Bar
   =========================== */
.chapter-nav {
    position: sticky;
    top: 70px; /* Below main header */
    background: var(--white, #ffffff);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.75rem clamp(0.75rem, 3vw, 3rem);
    margin-bottom: 1.5rem;
    gap: 1rem;
    z-index: 900;
    max-width: 100%;
    overflow: visible;
}

.chapter-nav-btn {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.25rem;
    background: var(--primary-color, #67A3B3);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    white-space: nowrap;
}

.chapter-nav-btn:hover:not(:disabled) {
    background: var(--primary-dark, #558899);
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

.chapter-nav-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.chapter-nav-btn .nav-arrow {
    font-size: 1.2rem;
    line-height: 1;
}

/* Dropdown */
.chapter-nav-dropdown {
    position: relative;
    flex: 1;
    max-width: 500px;
    overflow: visible;
}

.chapter-nav-current {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    padding: 0.75rem 1.25rem;
    background: var(--light-bg, #f7fbfc);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-color, #2c3e50);
    cursor: pointer;
    transition: all 0.3s ease;
    gap: 0.75rem;
}

.chapter-nav-current:hover {
    background: var(--white, #ffffff);
    border-color: var(--primary-dark, #558899);
}

.chapter-nav-current[aria-expanded="true"] {
    border-bottom-left-radius: 0;
    border-bottom-right-radius: 0;
    border-bottom-color: transparent;
}

.dropdown-icon {
    font-size: 1.2rem;
    line-height: 1;
}

.dropdown-label {
    flex: 1;
    text-align: left;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.dropdown-arrow {
    font-size: 0.875rem;
    transition: transform 0.3s ease;
}

.chapter-nav-current[aria-expanded="true"] .dropdown-arrow {
    transform: rotate(180deg);
}

.chapter-nav-menu {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--white, #ffffff);
    border: 1px solid var(--border-color);
    border-top: none;
    border-radius: 0 0 8px 8px;
    list-style: none;
    margin: 0;
    padding: 0;
    display: none;
    max-height: 400px;
    overflow-y: auto;
    z-index: 1001;
}

.chapter-nav-menu.active {
    display: block;
}

.chapter-nav-menu li {
    margin: 0;
}

.chapter-nav-menu button {
    display: block;
    width: 100%;
    padding: 0.875rem 1.25rem;
    text-align: left;
    background: none;
    border: none;
    border-bottom: 1px solid var(--border-color, #d9e7ec);
    font-size: 1rem;
    color: var(--text-color, #2c3e50);
    cursor: pointer;
    transition: background 0.2s ease;
}

.chapter-nav-menu li:last-child button {
    border-bottom: none;
    border-radius: 0 0 6px 6px;
}

.chapter-nav-menu button:hover {
    background: var(--light-bg, #f7fbfc);
}

.chapter-nav-menu button.current {
    background: var(--primary-color, #67A3B3);
    color: white;
    font-weight: 600;
}

.chapter-nav-menu button.current::before {
    content: '✓ ';
    margin-right: 0.5rem;
}

/* Mobile Responsive */
@media (max-width: 768px) {
    .chapter-nav {
        top: 60px; /* Adjust for smaller header */
        padding: 1rem 0.75rem;
        margin-top: 1rem;
        margin-bottom: 1rem;
        gap: 0.5rem;
        align-items: stretch;
        min-height: fit-content;
    }
    
    .chapter-nav-btn {
        padding: 0.875rem 0.75rem;
        font-size: 0.9rem;
        flex-shrink: 0;
        align-self: center;
    }
    
    .chapter-nav-btn .nav-label {
        display: none; /* Hide "Prev" and "Next" text on mobile */
    }
    
    .chapter-nav-btn .nav-arrow {
        font-size: 1.5rem;
    }
    
    .chapter-nav-dropdown {
        min-width: 0;
        flex-shrink: 1;
        flex-grow: 1;
        display: flex;
        align-items: stretch;
    }
    
    .chapter-nav-current {
        padding: 0.875rem 0.75rem;
        font-size: 0.875rem;
        align-items: center;
        min-width: 0;
        width: 100%;
        min-height: fit-content;
    }
    
    .dropdown-icon {
        font-size: 1rem;
        flex-shrink: 0;
        align-self: flex-start;
        margin-top: 0.1rem;
    }
    
    .dropdown-label {
        font-size: 0.875rem;
        white-space: normal;
        overflow-wrap: break-word;
        word-wrap: break-word;
        line-height: 1.3;
        min-width: 0;
        flex: 1;
    }
    
    .dropdown-arrow {
        flex-shrink: 0;
        align-self: flex-start;
        margin-top: 0.1rem;
    }
    
    .chapter-nav-menu button {
        padding: 0.75rem 1rem;
        font-size: 0.875rem;
        white-space: normal;
        overflow-wrap: break-word;
        word-wrap: break-word;
        line-height: 1.3;
    }
}

@media (max-width: 480px) {
    .chapter-nav {
        gap: 0.375rem;
    }
    
    .chapter-nav-btn {
        padding: 0.5rem 0.625rem;
    }
    
    .dropdown-icon {
        display: none; /* Hide icon on very small screens */
    }
}