/**
 * AI 小說平台 - 響應式 CSS 框架
 * Requirements: 13.1 - 響應式設計的閱讀介面
 */

/* ========================================
   CSS Variables (主題變數)
   ======================================== */
:root {
    /* 主色調 */
    --primary-color: #4a90d9;
    --primary-dark: #3a7bc8;
    --primary-light: #6ba3e0;
    
    /* 文字顏色 */
    --text-primary: #333333;
    --text-secondary: #666666;
    --text-muted: #999999;
    --text-light: #ffffff;
    
    /* 背景顏色 */
    --bg-primary: #ffffff;
    --bg-secondary: #f5f5f5;
    --bg-tertiary: #e8e8e8;
    --bg-dark: #2c3e50;
    
    /* 邊框顏色 */
    --border-color: #e0e0e0;
    --border-light: #f0f0f0;
    
    /* 狀態顏色 */
    --success-color: #28a745;
    --warning-color: #ffc107;
    --danger-color: #dc3545;
    --info-color: #17a2b8;
    
    /* 間距 */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;
    
    /* 字體 */
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans TC", sans-serif;
    --font-family-reading: "Noto Serif TC", Georgia, "Times New Roman", serif;
    
    /* 字體大小 */
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-xxl: 1.5rem;
    --font-size-xxxl: 2rem;
    
    /* 圓角 */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 12px;
    --border-radius-full: 9999px;
    
    /* 陰影 */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    
    /* 過渡 */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s ease;
    
    /* 容器寬度 */
    --container-max-width: 1200px;
    --container-narrow: 800px;
    
    /* Header 高度 */
    --header-height: 60px;
}

/* ========================================
   Reset & Base Styles
   ======================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-secondary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--primary-dark);
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

ul, ol {
    list-style: none;
}

button, input, select, textarea {
    font-family: inherit;
    font-size: inherit;
}

/* ========================================
   Layout Components
   ======================================== */
.container {
    width: 100%;
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.container-narrow {
    max-width: var(--container-narrow);
}

.main-content {
    flex: 1;
    padding: var(--spacing-lg) 0;
}

/* ========================================
   Grid System
   ======================================== */
.row {
    display: flex;
    flex-wrap: wrap;
    margin: 0 calc(var(--spacing-md) * -0.5);
}

.col {
    flex: 1;
    padding: 0 calc(var(--spacing-md) * 0.5);
}

.col-12 { flex: 0 0 100%; max-width: 100%; }
.col-6 { flex: 0 0 50%; max-width: 50%; }
.col-4 { flex: 0 0 33.333%; max-width: 33.333%; }
.col-3 { flex: 0 0 25%; max-width: 25%; }

/* ========================================
   Header Styles
   ======================================== */
.site-header {
    background-color: var(--bg-primary);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 1000;
    height: var(--header-height);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 100%;
}

.site-logo {
    display: flex;
    align-items: center;
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--primary-color);
}

.site-logo:hover {
    color: var(--primary-dark);
}

.site-logo img {
    height: 36px;
    margin-right: var(--spacing-sm);
}

/* Navigation */
.main-nav {
    display: flex;
    align-items: center;
}

.nav-list {
    display: flex;
    align-items: center;
    gap: var(--spacing-lg);
    list-style: none;
    margin: 0;
    padding: 0;
}

.nav-item a {
    color: var(--text-secondary);
    font-weight: 500;
    padding: var(--spacing-sm) 0;
    position: relative;
}

.nav-item a:hover,
.nav-item a.active {
    color: var(--primary-color);
}

.nav-item a.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 2px;
    background-color: var(--primary-color);
}

/* Mobile Menu Toggle */
.menu-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--spacing-sm);
}

.menu-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background-color: var(--text-primary);
    margin: 5px 0;
    transition: var(--transition-fast);
}

/* User Actions */
.user-actions {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

/* Language Switcher */
.language-switcher {
    display: flex;
    align-items: center;
}

.language-switcher button {
    min-width: 36px;
    height: 36px;
    padding: 0;
    font-weight: 600;
    font-size: var(--font-size-sm);
}

/* Notification Bell */
.notification-bell {
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    font-size: 1.25rem;
    text-decoration: none;
    border-radius: var(--border-radius-full);
    transition: var(--transition-fast);
}

.notification-bell:hover {
    background-color: var(--bg-tertiary);
}

.notification-badge {
    position: absolute;
    top: -2px;
    right: -2px;
    min-width: 18px;
    height: 18px;
    padding: 0 4px;
    font-size: 10px;
    font-weight: 600;
    line-height: 18px;
    text-align: center;
    color: white;
    background-color: var(--danger-color);
    border-radius: var(--border-radius-full);
}

.search-form {
    position: relative;
}

.search-input {
    width: 200px;
    padding: var(--spacing-sm) var(--spacing-md);
    padding-right: 36px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-full);
    outline: none;
    transition: var(--transition-fast);
}

.search-input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.1);
}

.search-btn {
    position: absolute;
    right: 8px;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    cursor: pointer;
    color: var(--text-muted);
}

/* ========================================
   Footer Styles
   ======================================== */
.site-footer {
    background-color: var(--bg-dark);
    color: var(--text-light);
    padding: var(--spacing-xl) 0;
    margin-top: auto;
}

.footer-inner {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    gap: var(--spacing-xl);
}

.footer-section {
    flex: 1;
    min-width: 200px;
}

.footer-section h4 {
    font-size: var(--font-size-lg);
    margin-bottom: var(--spacing-md);
    color: var(--text-light);
}

.footer-links {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.footer-links a {
    color: rgba(255, 255, 255, 0.7);
}

.footer-links a:hover {
    color: var(--text-light);
}

.footer-bottom {
    margin-top: var(--spacing-xl);
    padding-top: var(--spacing-lg);
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    text-align: center;
    color: rgba(255, 255, 255, 0.5);
    font-size: var(--font-size-sm);
}

/* ========================================
   Buttons
   ======================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-sm) var(--spacing-lg);
    border: none;
    border-radius: var(--border-radius-md);
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition-fast);
    text-decoration: none;
}

.btn-primary {
    background-color: var(--primary-color);
    color: var(--text-light);
}

.btn-primary:hover {
    background-color: var(--primary-dark);
    color: var(--text-light);
}

.btn-secondary {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background-color: var(--border-color);
}

.btn-outline {
    background-color: transparent;
    border: 1px solid var(--primary-color);
    color: var(--primary-color);
}

.btn-outline:hover {
    background-color: var(--primary-color);
    color: var(--text-light);
}

.btn-sm {
    padding: var(--spacing-xs) var(--spacing-md);
    font-size: var(--font-size-sm);
}

.btn-lg {
    padding: var(--spacing-md) var(--spacing-xl);
    font-size: var(--font-size-lg);
}

/* ========================================
   Cards
   ======================================== */
.card {
    background-color: var(--bg-primary);
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
    transition: var(--transition-normal);
}

.card:hover {
    box-shadow: var(--shadow-md);
}

.card-img {
    width: 100%;
    aspect-ratio: 3/4;
    object-fit: cover;
}

.card-body {
    padding: var(--spacing-md);
}

.card-title {
    font-size: var(--font-size-lg);
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.card-text {
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
}

/* Novel Card */
.novel-card {
    display: flex;
    flex-direction: column;
}

.novel-card .card-img {
    aspect-ratio: 3/4;
}

.novel-card .novel-meta {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
    margin-top: var(--spacing-sm);
}

.novel-card .author {
    color: var(--text-muted);
    font-size: var(--font-size-sm);
}

/* ========================================
   Tags
   ======================================== */
.tag {
    display: inline-block;
    padding: var(--spacing-xs) var(--spacing-sm);
    background-color: var(--bg-secondary);
    color: var(--text-secondary);
    font-size: var(--font-size-xs);
    border-radius: var(--border-radius-sm);
}

.tag-primary {
    background-color: rgba(74, 144, 217, 0.1);
    color: var(--primary-color);
}

.tag-success {
    background-color: rgba(40, 167, 69, 0.1);
    color: var(--success-color);
}

/* ========================================
   Forms
   ======================================== */
.form-group {
    margin-bottom: var(--spacing-md);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-xs);
    font-weight: 500;
    color: var(--text-primary);
}

.form-control {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-md);
    outline: none;
    transition: var(--transition-fast);
}

.form-control:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.1);
}

.form-control.error {
    border-color: var(--danger-color);
}

.form-control-color {
    width: 50px;
    height: 38px;
    padding: 2px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-md);
    cursor: pointer;
}

.form-range {
    width: 100%;
    height: 8px;
    -webkit-appearance: none;
    appearance: none;
    background: var(--bg-tertiary);
    border-radius: var(--border-radius-full);
    outline: none;
}

.form-range::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 20px;
    height: 20px;
    background: var(--primary-color);
    border-radius: 50%;
    cursor: pointer;
    transition: var(--transition-fast);
}

.form-range::-webkit-slider-thumb:hover {
    background: var(--primary-dark);
    transform: scale(1.1);
}

.form-range::-moz-range-thumb {
    width: 20px;
    height: 20px;
    background: var(--primary-color);
    border: none;
    border-radius: 50%;
    cursor: pointer;
}

.form-error {
    color: var(--danger-color);
    font-size: var(--font-size-sm);
    margin-top: var(--spacing-xs);
}

/* ========================================
   Alerts
   ======================================== */
.alert {
    padding: var(--spacing-md);
    border-radius: var(--border-radius-md);
    margin-bottom: var(--spacing-md);
}

.alert-success {
    background-color: rgba(40, 167, 69, 0.1);
    color: var(--success-color);
    border: 1px solid rgba(40, 167, 69, 0.2);
}

.alert-danger {
    background-color: rgba(220, 53, 69, 0.1);
    color: var(--danger-color);
    border: 1px solid rgba(220, 53, 69, 0.2);
}

.alert-warning {
    background-color: rgba(255, 193, 7, 0.1);
    color: #856404;
    border: 1px solid rgba(255, 193, 7, 0.2);
}

.alert-info {
    background-color: rgba(23, 162, 184, 0.1);
    color: var(--info-color);
    border: 1px solid rgba(23, 162, 184, 0.2);
}

/* ========================================
   Pagination
   ======================================== */
.pagination {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: var(--spacing-xs);
    margin-top: var(--spacing-xl);
}

.pagination a,
.pagination span {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 36px;
    height: 36px;
    padding: 0 var(--spacing-sm);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    color: var(--text-secondary);
    transition: var(--transition-fast);
}

.pagination a:hover {
    background-color: var(--bg-secondary);
    border-color: var(--primary-color);
    color: var(--primary-color);
}

.pagination .active {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
    color: var(--text-light);
}

.pagination .disabled {
    opacity: 0.5;
    pointer-events: none;
}

/* ========================================
   Utilities
   ======================================== */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.text-primary { color: var(--primary-color); }
.text-secondary { color: var(--text-secondary); }
.text-muted { color: var(--text-muted); }
.text-success { color: var(--success-color); }
.text-danger { color: var(--danger-color); }

.mt-0 { margin-top: 0; }
.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }
.mt-4 { margin-top: var(--spacing-xl); }

.mb-0 { margin-bottom: 0; }
.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }
.mb-4 { margin-bottom: var(--spacing-xl); }

.p-0 { padding: 0; }
.p-1 { padding: var(--spacing-sm); }
.p-2 { padding: var(--spacing-md); }
.p-3 { padding: var(--spacing-lg); }
.p-4 { padding: var(--spacing-xl); }

.d-none { display: none; }
.d-block { display: block; }
.d-flex { display: flex; }
.d-inline { display: inline; }
.d-inline-block { display: inline-block; }

.flex-wrap { flex-wrap: wrap; }
.justify-between { justify-content: space-between; }
.justify-center { justify-content: center; }
.align-center { align-items: center; }
.gap-1 { gap: var(--spacing-sm); }
.gap-2 { gap: var(--spacing-md); }
.gap-3 { gap: var(--spacing-lg); }

.w-100 { width: 100%; }
.h-100 { height: 100%; }

.truncate {
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.line-clamp-2 {
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.line-clamp-3 {
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

/* ========================================
   Responsive Breakpoints
   ======================================== */

/* Tablet (768px and up) */
@media (max-width: 991px) {
    .col-md-12 { flex: 0 0 100%; max-width: 100%; }
    .col-md-6 { flex: 0 0 50%; max-width: 50%; }
    .col-md-4 { flex: 0 0 33.333%; max-width: 33.333%; }
    
    .nav-list {
        gap: var(--spacing-md);
    }
    
    .search-input {
        width: 160px;
    }
}

/* Mobile (767px and below) */
@media (max-width: 767px) {
    :root {
        --header-height: 56px;
    }
    
    .menu-toggle {
        display: block;
    }
    
    .main-nav {
        position: fixed;
        top: var(--header-height);
        left: 0;
        right: 0;
        bottom: 0;
        background-color: var(--bg-primary);
        padding: var(--spacing-lg);
        transform: translateX(-100%);
        transition: transform var(--transition-normal);
        z-index: 999;
    }
    
    .main-nav.active {
        transform: translateX(0);
    }
    
    .nav-list {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-md);
    }
    
    .nav-item {
        width: 100%;
    }
    
    .nav-item a {
        display: block;
        padding: var(--spacing-md);
        border-bottom: 1px solid var(--border-light);
    }
    
    .search-form {
        display: none;
    }
    
    .mobile-search {
        display: block;
        padding: var(--spacing-md);
        border-bottom: 1px solid var(--border-light);
    }
    
    .mobile-search .search-input {
        width: 100%;
    }
    
    .user-actions {
        gap: var(--spacing-sm);
    }
    
    .col-sm-12 { flex: 0 0 100%; max-width: 100%; }
    .col-sm-6 { flex: 0 0 50%; max-width: 50%; }
    
    .footer-inner {
        flex-direction: column;
        text-align: center;
    }
    
    .footer-section {
        min-width: 100%;
    }
    
    .d-sm-none { display: none; }
    .d-sm-block { display: block; }
}

/* Small Mobile (480px and below) */
@media (max-width: 480px) {
    html {
        font-size: 14px;
    }
    
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .col-xs-12 { flex: 0 0 100%; max-width: 100%; }
    .col-xs-6 { flex: 0 0 50%; max-width: 50%; }
    
    .btn {
        padding: var(--spacing-sm) var(--spacing-md);
    }
}

/* ========================================
   Novel Grid Layout
   ======================================== */
.novel-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
    gap: var(--spacing-lg);
}

@media (max-width: 767px) {
    .novel-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-md);
    }
}

@media (max-width: 480px) {
    .novel-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-sm);
    }
}

/* ========================================
   Ranking List
   ======================================== */
.ranking-list {
    background-color: var(--bg-primary);
    border-radius: var(--border-radius-md);
    overflow: hidden;
}

.ranking-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--border-light);
}

.ranking-title {
    font-size: var(--font-size-lg);
    font-weight: 600;
}

.ranking-more {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
}

.ranking-item {
    display: flex;
    align-items: center;
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--border-light);
    transition: background-color var(--transition-fast);
}

.ranking-item:last-child {
    border-bottom: none;
}

.ranking-item:hover {
    background-color: var(--bg-secondary);
}

.ranking-rank {
    width: 28px;
    height: 28px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    margin-right: var(--spacing-md);
}

.ranking-rank.top-1 { color: #ffd700; }
.ranking-rank.top-2 { color: #c0c0c0; }
.ranking-rank.top-3 { color: #cd7f32; }

.ranking-cover {
    width: 48px;
    height: 64px;
    object-fit: cover;
    border-radius: var(--border-radius-sm);
    margin-right: var(--spacing-md);
}

.ranking-info {
    flex: 1;
    min-width: 0;
}

.ranking-novel-title {
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.ranking-novel-title:hover {
    color: var(--primary-color);
}

.ranking-meta {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
}

/* ========================================
   Section Headers
   ======================================== */
.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
}

.section-title {
    font-size: var(--font-size-xxl);
    font-weight: 700;
    color: var(--text-primary);
}

.section-more {
    color: var(--text-muted);
    font-size: var(--font-size-sm);
}

.section-more:hover {
    color: var(--primary-color);
}

/* ========================================
   Loading States
   ======================================== */
.loading {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: var(--spacing-xl);
}

.spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--border-color);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* ========================================
   Empty States
   ======================================== */
.empty-state {
    text-align: center;
    padding: var(--spacing-xxl);
    color: var(--text-muted);
}

.empty-state-icon {
    font-size: 48px;
    margin-bottom: var(--spacing-md);
    opacity: 0.5;
}

.empty-state-text {
    font-size: var(--font-size-lg);
}

/* ========================================
   Breadcrumb Navigation
   Requirements: 6.1, 6.4 - 麵包屑導航系統
   ======================================== */
.breadcrumb-nav {
    padding: var(--spacing-md) 0;
    margin-bottom: var(--spacing-md);
}

.breadcrumb-list {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0;
    margin: 0;
    padding: 0;
    list-style: none;
    font-size: var(--font-size-sm);
}

.breadcrumb-item {
    display: flex;
    align-items: center;
}

.breadcrumb-item a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color var(--transition-fast);
    padding: var(--spacing-xs) 0;
}

.breadcrumb-item a:hover {
    color: var(--primary-color);
    text-decoration: underline;
}

.breadcrumb-item-current span {
    color: var(--text-muted);
    font-weight: 500;
}

.breadcrumb-separator {
    color: var(--text-muted);
    margin: 0 var(--spacing-sm);
    user-select: none;
}

/* Compact breadcrumb for mobile */
@media (max-width: 767px) {
    .breadcrumb-nav {
        padding: var(--spacing-sm) 0;
    }
    
    .breadcrumb-list {
        font-size: var(--font-size-xs);
    }
    
    .breadcrumb-separator {
        margin: 0 var(--spacing-xs);
    }
}

/* Legacy breadcrumb support */
.breadcrumb {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) 0;
    font-size: var(--font-size-sm);
    color: var(--text-muted);
}

.breadcrumb a {
    color: var(--text-secondary);
}

.breadcrumb a:hover {
    color: var(--primary-color);
}

/* ========================================
   Modal
   ======================================== */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 2000;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-normal);
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal {
    background-color: var(--bg-primary);
    border-radius: var(--border-radius-lg);
    max-width: 500px;
    width: 90%;
    max-height: 90vh;
    overflow-y: auto;
    transform: translateY(-20px);
    transition: var(--transition-normal);
}

.modal-overlay.active .modal {
    transform: translateY(0);
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-lg);
    border-bottom: 1px solid var(--border-light);
}

.modal-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
}

.modal-close {
    background: none;
    border: none;
    font-size: var(--font-size-xl);
    cursor: pointer;
    color: var(--text-muted);
    padding: var(--spacing-xs);
}

.modal-close:hover {
    color: var(--text-primary);
}

.modal-body {
    padding: var(--spacing-lg);
}

.modal-footer {
    display: flex;
    justify-content: flex-end;
    gap: var(--spacing-md);
    padding: var(--spacing-lg);
    border-top: 1px solid var(--border-light);
}


/* ========================================
   Lazy Loading Images
   Requirements: 15.3 - 使用 lazy loading 延遲載入圖片
   ======================================== */

/* Lazy image placeholder */
img.lazy {
    opacity: 0;
    transition: opacity var(--transition-normal);
    background-color: var(--bg-tertiary);
}

/* Lazy image loaded state */
img.lazy-loaded {
    opacity: 1;
}

/* Placeholder for lazy images */
.lazy-placeholder {
    position: relative;
    background-color: var(--bg-tertiary);
    overflow: hidden;
}

.lazy-placeholder::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(
        90deg,
        transparent,
        rgba(255, 255, 255, 0.4),
        transparent
    );
    animation: shimmer 1.5s infinite;
}

@keyframes shimmer {
    0% {
        left: -100%;
    }
    100% {
        left: 100%;
    }
}

/* Native lazy loading support indicator */
img[loading="lazy"] {
    /* Browser handles lazy loading natively */
}

/* Blur-up effect for lazy images */
img.lazy-blur {
    filter: blur(10px);
    transition: filter var(--transition-normal), opacity var(--transition-normal);
}

img.lazy-blur.lazy-loaded {
    filter: blur(0);
}


/* ========================================
   Navigation Dropdown Menus
   Requirements: 6.2, 6.3 - 選單層級結構與摺疊
   ======================================== */

/* Nav Item Dropdown */
.nav-item-dropdown {
    position: relative;
}

.nav-item-dropdown > a {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.nav-dropdown-arrow {
    font-size: 0.625rem;
    transition: transform var(--transition-fast);
}

.nav-item-dropdown:hover .nav-dropdown-arrow {
    transform: rotate(180deg);
}

.nav-dropdown-menu {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    min-width: 150px;
    background-color: var(--bg-primary);
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-lg);
    padding: var(--spacing-sm) 0;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all var(--transition-fast);
    z-index: 1001;
    list-style: none;
}

.nav-item-dropdown:hover .nav-dropdown-menu {
    display: block;
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.nav-dropdown-menu li a {
    display: block;
    padding: var(--spacing-sm) var(--spacing-md);
    color: var(--text-secondary);
    white-space: nowrap;
    transition: all var(--transition-fast);
}

.nav-dropdown-menu li a:hover,
.nav-dropdown-menu li a.active {
    background-color: var(--bg-secondary);
    color: var(--primary-color);
}

/* User Dropdown */
.user-dropdown {
    position: relative;
}

.user-dropdown-toggle {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    cursor: pointer;
}

.user-dropdown-arrow {
    font-size: 0.625rem;
    transition: transform var(--transition-fast);
}

.user-dropdown.active .user-dropdown-arrow {
    transform: rotate(180deg);
}

.user-dropdown-menu {
    display: none;
    position: absolute;
    top: calc(100% + 5px);
    right: 0;
    min-width: 180px;
    background-color: var(--bg-primary);
    border-radius: var(--border-radius-md);
    box-shadow: var(--shadow-lg);
    padding: var(--spacing-sm) 0;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all var(--transition-fast);
    z-index: 1001;
    list-style: none;
}

.user-dropdown.active .user-dropdown-menu {
    display: block;
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.user-dropdown-menu li a {
    display: block;
    padding: var(--spacing-sm) var(--spacing-md);
    color: var(--text-secondary);
    white-space: nowrap;
    transition: all var(--transition-fast);
}

.user-dropdown-menu li a:hover {
    background-color: var(--bg-secondary);
    color: var(--primary-color);
}

.user-dropdown-menu .divider {
    height: 1px;
    background-color: var(--border-light);
    margin: var(--spacing-sm) 0;
}

/* Mobile Navigation Adjustments */
@media (max-width: 767px) {
    /* 手機版：下拉選單預設隱藏，點擊後展開 */
    .nav-dropdown-menu {
        position: static;
        max-height: 0;
        overflow: hidden;
        opacity: 0;
        visibility: hidden;
        transform: none;
        box-shadow: none;
        background-color: var(--bg-secondary);
        border-radius: 0;
        padding: 0;
        margin-left: var(--spacing-lg);
        transition: max-height var(--transition-normal), opacity var(--transition-fast), visibility var(--transition-fast);
    }
    
    /* 手機版：展開狀態 */
    .nav-item-dropdown.active .nav-dropdown-menu {
        max-height: 200px;
        opacity: 1;
        visibility: visible;
    }
    
    .nav-dropdown-menu li a {
        padding: var(--spacing-sm) var(--spacing-md);
        border-bottom: 1px solid var(--border-light);
    }
    
    .user-dropdown-menu {
        position: fixed;
        top: auto;
        bottom: 0;
        left: 0;
        right: 0;
        border-radius: var(--border-radius-lg) var(--border-radius-lg) 0 0;
        min-width: 100%;
    }
}


/* ========================================
   AdSense 廣告容器樣式
   Requirements: 4.1, 4.2, 4.3 - 廣告版位響應式設計
   ======================================== */

/* 廣告容器基礎樣式 */
.ad-container {
    display: flex;
    align-items: center;
    justify-content: center;
    margin: var(--spacing-lg) auto;
    overflow: hidden;
}

/* 300x250 廣告單元 */
.ad-300x250 {
    width: 300px;
    height: 250px;
    min-width: 300px;
    min-height: 250px;
}

/* 廣告佔位區塊 */
.ad-placeholder {
    width: 100%;
    height: 100%;
    background-color: var(--bg-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    font-size: var(--font-size-sm);
    border: 1px dashed var(--border-color);
    border-radius: var(--border-radius-sm);
}

/* 內容頂部廣告 */
.ad-content-top {
    margin-top: 0;
    margin-bottom: var(--spacing-lg);
}

/* 內容底部廣告 */
.ad-content-bottom {
    margin-top: var(--spacing-lg);
    margin-bottom: 0;
}

/* 排行榜內嵌廣告 */
.ad-ranking-inline {
    margin: var(--spacing-md) auto;
    padding: var(--spacing-md) 0;
    border-top: 1px solid var(--border-light);
    border-bottom: 1px solid var(--border-light);
    background-color: var(--bg-secondary);
}

/* 響應式設計：平板裝置 */
@media (max-width: 991px) {
    .ad-container {
        margin: var(--spacing-md) auto;
    }
}

/* 響應式設計：行動裝置 */
@media (max-width: 767px) {
    .ad-container {
        margin: var(--spacing-md) auto;
    }
    
    /* 行動裝置上廣告置中顯示 */
    .ad-300x250 {
        max-width: 100%;
    }
    
    /* 閱讀頁面廣告間距調整 */
    .ad-content-top,
    .ad-content-bottom {
        margin-left: calc(var(--spacing-md) * -1);
        margin-right: calc(var(--spacing-md) * -1);
        width: calc(100% + var(--spacing-md) * 2);
        display: flex;
        justify-content: center;
    }
}

/* 小型行動裝置 */
@media (max-width: 480px) {
    .ad-container {
        margin: var(--spacing-sm) auto;
    }
}