/* ============================================
   零起点学针灸 — 全局样式
   ============================================ */

/* ---------- CSS Variables ---------- */
:root {
    /* 颜色 */
    --color-primary: #2C5F2D;
    --color-primary-light: #3A7D3E;
    --color-primary-dark: #1E4220;
    --color-secondary: #97BC62;
    --color-secondary-light: #B5D48B;
    --color-accent: #C75146;
    --color-accent-light: #E07B72;
    --color-bg: #FAF8F0;
    --color-bg-card: #FFFFFF;
    --color-bg-code: #F5F2E8;
    --color-text: #333333;
    --color-text-light: #666666;
    --color-text-muted: #999999;
    --color-border: #E8E4D8;
    --color-border-light: #F0EDE4;
    --color-shadow: rgba(44, 95, 45, 0.08);
    --color-gold: #B8860B;

    /* 字体 */
    --font-heading: 'LXGW WenKai', 'Noto Serif SC', 'STSong', 'SimSun', serif;
    --font-body: 'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
    --font-quote: 'LXGW WenKai', 'KaiTi', 'STKaiti', serif;
    --font-mono: 'Fira Code', 'Consolas', monospace;

    /* 间距 */
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-2xl: 48px;
    --spacing-3xl: 64px;

    /* 圆角 */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;

    /* 过渡 */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;

    /* 阴影 */
    --shadow-sm: 0 1px 3px var(--color-shadow);
    --shadow-md: 0 4px 12px var(--color-shadow);
    --shadow-lg: 0 8px 24px var(--color-shadow);

    /* 最大宽度 */
    --max-width: 960px;
    --max-width-wide: 1200px;

    /* 侧边栏 */
    --sidebar-width: 260px;
}

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

html {
    font-size: 16px;
    scroll-behavior: smooth;
    scroll-padding-top: 80px;
}

body {
    font-family: var(--font-body);
    color: var(--color-text);
    background-color: var(--color-bg);
    line-height: 1.8;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

a:hover {
    color: var(--color-accent);
}

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

/* ---------- Typography ---------- */
h1,
h2,
h3,
h4,
h5,
h6 {
    font-family: var(--font-heading);
    font-weight: 700;
    line-height: 1.4;
    color: var(--color-primary-dark);
}

h1 {
    font-size: 2.2rem;
    margin-bottom: var(--spacing-lg);
}

h2 {
    font-size: 1.75rem;
    margin-bottom: var(--spacing-md);
}

h3 {
    font-size: 1.35rem;
    margin-bottom: var(--spacing-md);
}

h4 {
    font-size: 1.15rem;
    margin-bottom: var(--spacing-sm);
}

p {
    margin-bottom: var(--spacing-md);
    text-align: justify;
}

blockquote {
    font-family: var(--font-quote);
    background: linear-gradient(135deg, var(--color-bg-code), transparent);
    border-left: 4px solid var(--color-secondary);
    padding: var(--spacing-md) var(--spacing-lg);
    margin: var(--spacing-lg) 0;
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    color: var(--color-text-light);
    font-size: 1.05rem;
    position: relative;
}

blockquote::before {
    content: '"';
    font-size: 3rem;
    color: var(--color-secondary-light);
    position: absolute;
    top: -8px;
    left: 12px;
    font-family: var(--font-heading);
}

/* ---------- Header / Navigation ---------- */
.site-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(250, 248, 240, 0.95);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--color-border-light);
    transition: box-shadow var(--transition-normal);
}

.site-header.scrolled {
    box-shadow: var(--shadow-md);
}

.header-inner {
    max-width: var(--max-width-wide);
    margin: 0 auto;
    padding: var(--spacing-sm) var(--spacing-lg);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.site-logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-family: var(--font-heading);
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--color-primary);
}

.site-logo .logo-icon {
    font-size: 1.6rem;
}

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

.nav-links a {
    font-size: 0.95rem;
    color: var(--color-text-light);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
    position: relative;
}

.nav-links a:hover,
.nav-links a.active {
    color: var(--color-primary);
    background: rgba(44, 95, 45, 0.06);
}

.nav-links a.active::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 50%;
    transform: translateX(-50%);
    width: 20px;
    height: 2px;
    background: var(--color-primary);
    border-radius: 1px;
}

/* 移动端菜单按钮 */
.menu-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--spacing-sm);
}

.menu-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--color-text);
    border-radius: 1px;
    transition: all var(--transition-fast);
}

/* 进度指示器 (header中) */
.header-progress {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 0.8rem;
    color: var(--color-text-muted);
}

.header-progress-bar {
    width: 60px;
    height: 4px;
    background: var(--color-border);
    border-radius: 2px;
    overflow: hidden;
}

.header-progress-fill {
    height: 100%;
    background: var(--color-secondary);
    border-radius: 2px;
    transition: width var(--transition-normal);
}

/* ---------- Reading Progress Bar ---------- */
.reading-progress-bar {
    position: fixed;
    top: 56px;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--color-border-light);
    z-index: 999;
}

.reading-progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--color-primary), var(--color-secondary));
    width: 0%;
    transition: width 0.1s linear;
}

/* ---------- Hero Section (Home) ---------- */
.hero {
    min-height: 85vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: var(--spacing-3xl) var(--spacing-lg);
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background:
        radial-gradient(circle at 20% 50%, rgba(151, 188, 98, 0.08) 0%, transparent 50%),
        radial-gradient(circle at 80% 20%, rgba(44, 95, 45, 0.05) 0%, transparent 40%),
        radial-gradient(circle at 50% 80%, rgba(199, 81, 70, 0.04) 0%, transparent 40%);
    pointer-events: none;
}

.hero-content {
    position: relative;
    z-index: 1;
    max-width: 700px;
}

.hero-subtitle {
    font-family: var(--font-quote);
    font-size: 1.1rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-md);
    letter-spacing: 2px;
}

.hero-title {
    font-size: 3rem;
    color: var(--color-primary-dark);
    margin-bottom: var(--spacing-md);
    letter-spacing: 4px;
}

.hero-title .accent {
    color: var(--color-accent);
}

.hero-desc {
    font-size: 1.1rem;
    color: var(--color-text-light);
    margin-bottom: var(--spacing-xl);
    line-height: 2;
}

.hero-cta {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-xl);
    background: var(--color-primary);
    color: #fff;
    border-radius: var(--radius-lg);
    font-size: 1.05rem;
    font-weight: 500;
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-md);
}

.hero-cta:hover {
    background: var(--color-primary-light);
    color: #fff;
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

/* 装饰性浮动元素 */
.floating-element {
    position: absolute;
    opacity: 0.15;
    font-size: 4rem;
    animation: floatAnimation 6s ease-in-out infinite;
    pointer-events: none;
}

.floating-element:nth-child(1) {
    top: 15%;
    left: 8%;
    animation-delay: 0s;
}

.floating-element:nth-child(2) {
    top: 60%;
    right: 10%;
    animation-delay: 2s;
}

.floating-element:nth-child(3) {
    bottom: 15%;
    left: 15%;
    animation-delay: 4s;
}

@keyframes floatAnimation {

    0%,
    100% {
        transform: translateY(0) rotate(0deg);
    }

    50% {
        transform: translateY(-20px) rotate(5deg);
    }
}

/* ---------- Section ---------- */
.section {
    padding: var(--spacing-3xl) var(--spacing-lg);
    max-width: var(--max-width);
    margin: 0 auto;
}

.section-wide {
    max-width: var(--max-width-wide);
}

.section-title {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    position: relative;
}

.section-title h2 {
    display: inline-block;
    position: relative;
}

.section-title h2::after {
    content: '';
    position: absolute;
    bottom: -8px;
    left: 50%;
    transform: translateX(-50%);
    width: 40px;
    height: 3px;
    background: var(--color-secondary);
    border-radius: 2px;
}

.section-title p {
    color: var(--color-text-muted);
    margin-top: var(--spacing-md);
    font-size: 0.95rem;
}

/* ---------- Learning Path / Chapter Cards ---------- */
.chapter-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: var(--spacing-lg);
}

.chapter-card {
    background: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    border: 1px solid var(--color-border-light);
    transition: all var(--transition-normal);
    cursor: pointer;
    position: relative;
    overflow: hidden;
}

.chapter-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: var(--color-border);
    transition: background var(--transition-normal);
}

.chapter-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: var(--color-secondary-light);
}

.chapter-card:hover::before {
    background: var(--color-primary);
}

.chapter-card.completed::before {
    background: var(--color-secondary);
}

.chapter-card .card-number {
    font-family: var(--font-heading);
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--color-border);
    line-height: 1;
    margin-bottom: var(--spacing-sm);
    transition: color var(--transition-normal);
}

.chapter-card:hover .card-number {
    color: var(--color-secondary-light);
}

.chapter-card .card-title {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    color: var(--color-primary-dark);
    margin-bottom: var(--spacing-sm);
}

.chapter-card .card-desc {
    font-size: 0.9rem;
    color: var(--color-text-light);
    line-height: 1.7;
    margin-bottom: var(--spacing-md);
}

.chapter-card .card-meta {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-size: 0.8rem;
    color: var(--color-text-muted);
}

.card-tag {
    display: inline-block;
    padding: 2px 10px;
    background: rgba(44, 95, 45, 0.06);
    color: var(--color-primary);
    border-radius: 20px;
    font-size: 0.75rem;
}

.card-progress {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.card-progress-bar {
    width: 40px;
    height: 3px;
    background: var(--color-border);
    border-radius: 2px;
    overflow: hidden;
}

.card-progress-fill {
    height: 100%;
    background: var(--color-secondary);
    border-radius: 2px;
}

/* 完成状态勾选 */
.chapter-card .card-check {
    position: absolute;
    top: var(--spacing-md);
    right: var(--spacing-md);
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: var(--color-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    color: #fff;
    font-size: 0.75rem;
    opacity: 0;
    transition: opacity var(--transition-normal);
}

.chapter-card.completed .card-check {
    opacity: 1;
}

/* ---------- Chapter Content Page ---------- */
.chapter-page {
    display: flex;
    max-width: var(--max-width-wide);
    margin: 0 auto;
    padding-top: 60px;
}

.chapter-sidebar {
    position: fixed;
    top: 60px;
    left: 0;
    width: var(--sidebar-width);
    height: calc(100vh - 60px);
    padding: var(--spacing-lg);
    background: var(--color-bg-card);
    border-right: 1px solid var(--color-border-light);
    overflow-y: auto;
    transition: transform var(--transition-normal);
    z-index: 100;
}

.chapter-sidebar .sidebar-title {
    font-family: var(--font-heading);
    font-size: 0.9rem;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 2px;
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid var(--color-border-light);
}

.sidebar-nav {
    list-style: none;
}

.sidebar-nav li {
    margin-bottom: var(--spacing-xs);
}

.sidebar-nav a {
    display: block;
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.9rem;
    color: var(--color-text-light);
    border-radius: var(--radius-sm);
    border-left: 3px solid transparent;
    transition: all var(--transition-fast);
}

.sidebar-nav a:hover {
    background: rgba(44, 95, 45, 0.04);
    color: var(--color-primary);
}

.sidebar-nav a.active {
    background: rgba(44, 95, 45, 0.08);
    color: var(--color-primary);
    border-left-color: var(--color-primary);
    font-weight: 500;
}

.sidebar-nav .sub-item a {
    padding-left: var(--spacing-xl);
    font-size: 0.85rem;
}

.chapter-content {
    flex: 1;
    margin-left: var(--sidebar-width);
    padding: var(--spacing-2xl) var(--spacing-2xl);
    max-width: calc(100% - var(--sidebar-width));
}

.chapter-header {
    margin-bottom: var(--spacing-2xl);
    padding-bottom: var(--spacing-lg);
    border-bottom: 2px solid var(--color-border-light);
}

.chapter-header .chapter-label {
    font-family: var(--font-heading);
    font-size: 0.9rem;
    color: var(--color-secondary);
    letter-spacing: 2px;
    margin-bottom: var(--spacing-sm);
}

.chapter-header h1 {
    font-size: 2.2rem;
    margin-bottom: var(--spacing-md);
}

.chapter-header .chapter-intro {
    font-size: 1.05rem;
    color: var(--color-text-light);
    line-height: 1.9;
}

/* 内容区段 */
.content-section {
    margin-bottom: var(--spacing-3xl);
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.6s ease;
}

.content-section.visible {
    opacity: 1;
    transform: translateY(0);
}

/* ---------- Term Tooltip (术语卡片) ---------- */
.term {
    color: var(--color-primary);
    border-bottom: 1px dashed var(--color-secondary);
    cursor: help;
    position: relative;
}

.term-tooltip {
    position: fixed;
    z-index: 2000;
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    max-width: 320px;
    box-shadow: var(--shadow-lg);
    font-size: 0.88rem;
    line-height: 1.7;
    pointer-events: none;
}

.term-tooltip .tooltip-title {
    font-family: var(--font-heading);
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: var(--spacing-xs);
    font-size: 0.95rem;
}

.term-tooltip .tooltip-body {
    color: var(--color-text-light);
}

/* ---------- Key Point Box (重点框) ---------- */
.key-point {
    background: linear-gradient(135deg, rgba(44, 95, 45, 0.04), rgba(151, 188, 98, 0.06));
    border: 1px solid rgba(44, 95, 45, 0.12);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin: var(--spacing-lg) 0;
    position: relative;
}

.key-point::before {
    content: '💡';
    position: absolute;
    top: -12px;
    left: var(--spacing-md);
    background: var(--color-bg);
    padding: 0 var(--spacing-sm);
    font-size: 1.2rem;
}

.key-point .key-title {
    font-family: var(--font-heading);
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: var(--spacing-sm);
    font-size: 1rem;
}

/* ---------- Expand Block (折叠展开) ---------- */
.expand-block {
    border: 1px solid var(--color-border-light);
    border-radius: var(--radius-md);
    margin: var(--spacing-md) 0;
    overflow: hidden;
}

.expand-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md) var(--spacing-lg);
    cursor: pointer;
    background: rgba(250, 248, 240, 0.5);
    transition: background var(--transition-fast);
    user-select: none;
}

.expand-header:hover {
    background: rgba(44, 95, 45, 0.04);
}

.expand-header .expand-title {
    font-family: var(--font-heading);
    font-size: 0.95rem;
    color: var(--color-primary);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.expand-header .expand-icon {
    font-size: 0.8rem;
    transition: transform var(--transition-fast);
    color: var(--color-text-muted);
}

.expand-block.open .expand-icon {
    transform: rotate(90deg);
}

.expand-body {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s ease, padding 0.3s ease;
    padding: 0 var(--spacing-lg);
}

.expand-block.open .expand-body {
    max-height: 2000px;
    padding: var(--spacing-md) var(--spacing-lg) var(--spacing-lg);
}

/* ---------- Note / Annotation (注释) ---------- */
.annotation {
    background: rgba(184, 134, 11, 0.06);
    border-left: 3px solid var(--color-gold);
    padding: var(--spacing-md) var(--spacing-lg);
    margin: var(--spacing-md) 0;
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    font-size: 0.9rem;
    color: var(--color-text-light);
}

.annotation .annotation-label {
    font-weight: 700;
    color: var(--color-gold);
    margin-bottom: var(--spacing-xs);
    font-size: 0.85rem;
}

/* ---------- Quiz (小测验) ---------- */
.quiz-block {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin: var(--spacing-xl) 0;
}

.quiz-block .quiz-title {
    font-family: var(--font-heading);
    font-size: 1.1rem;
    color: var(--color-primary);
    margin-bottom: var(--spacing-md);
}

.quiz-option {
    display: block;
    padding: var(--spacing-sm) var(--spacing-md);
    margin-bottom: var(--spacing-sm);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-size: 0.95rem;
}

.quiz-option:hover {
    background: rgba(44, 95, 45, 0.04);
    border-color: var(--color-secondary);
}

.quiz-option.correct {
    background: rgba(151, 188, 98, 0.15);
    border-color: var(--color-secondary);
    color: var(--color-primary-dark);
}

.quiz-option.wrong {
    background: rgba(199, 81, 70, 0.08);
    border-color: var(--color-accent-light);
    color: var(--color-accent);
}

.quiz-feedback {
    margin-top: var(--spacing-md);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: 0.9rem;
    display: none;
}

.quiz-feedback.show {
    display: block;
}

.quiz-feedback.correct {
    background: rgba(151, 188, 98, 0.1);
    color: var(--color-primary-dark);
}

.quiz-feedback.wrong {
    background: rgba(199, 81, 70, 0.08);
    color: var(--color-accent);
}

/* ---------- Chapter Navigation (上/下章节) ---------- */
.chapter-nav {
    display: flex;
    justify-content: space-between;
    gap: var(--spacing-lg);
    padding: var(--spacing-2xl) 0;
    margin-top: var(--spacing-2xl);
    border-top: 1px solid var(--color-border-light);
}

.chapter-nav-item {
    flex: 1;
    padding: var(--spacing-lg);
    background: var(--color-bg-card);
    border: 1px solid var(--color-border-light);
    border-radius: var(--radius-lg);
    transition: all var(--transition-normal);
    text-decoration: none;
}

.chapter-nav-item:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--color-secondary-light);
    transform: translateY(-2px);
}

.chapter-nav-item .nav-label {
    font-size: 0.8rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-xs);
}

.chapter-nav-item .nav-title {
    font-family: var(--font-heading);
    font-size: 1.05rem;
    color: var(--color-primary);
}

.chapter-nav-item.next {
    text-align: right;
}

/* ---------- Footer ---------- */
.site-footer {
    background: var(--color-primary-dark);
    color: rgba(255, 255, 255, 0.7);
    padding: var(--spacing-2xl) var(--spacing-lg);
    text-align: center;
    font-size: 0.85rem;
}

.site-footer .footer-inner {
    max-width: var(--max-width);
    margin: 0 auto;
}

.site-footer .disclaimer {
    padding: var(--spacing-md);
    margin-bottom: var(--spacing-md);
    background: rgba(199, 81, 70, 0.15);
    border: 1px solid rgba(199, 81, 70, 0.3);
    border-radius: var(--radius-md);
    color: rgba(255, 255, 255, 0.85);
    font-size: 0.8rem;
    line-height: 1.7;
}

.site-footer .disclaimer strong {
    color: var(--color-accent-light);
}

.footer-links {
    display: flex;
    justify-content: center;
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
    flex-wrap: wrap;
}

.footer-links a {
    color: rgba(255, 255, 255, 0.6);
    font-size: 0.85rem;
}

.footer-links a:hover {
    color: #fff;
}

/* ---------- Modal (安全声明弹窗) ---------- */
.modal-overlay {
    position: fixed;
    inset: 0;
    z-index: 3000;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-lg);
    backdrop-filter: blur(4px);
}

.modal-box {
    background: var(--color-bg-card);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    max-width: 520px;
    width: 100%;
    box-shadow: var(--shadow-lg);
    text-align: center;
}

.modal-box .modal-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.modal-box h2 {
    margin-bottom: var(--spacing-md);
}

.modal-box p {
    font-size: 0.95rem;
    color: var(--color-text-light);
    text-align: left;
    margin-bottom: var(--spacing-md);
}

.modal-btn {
    display: inline-block;
    padding: var(--spacing-sm) var(--spacing-xl);
    background: var(--color-primary);
    color: #fff;
    border: none;
    border-radius: var(--radius-md);
    font-size: 1rem;
    cursor: pointer;
    transition: background var(--transition-fast);
    font-family: var(--font-body);
}

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

/* ---------- Back to Top ---------- */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 44px;
    height: 44px;
    background: var(--color-primary);
    color: #fff;
    border: none;
    border-radius: 50%;
    font-size: 1.2rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-md);
    z-index: 500;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:hover {
    background: var(--color-primary-light);
    transform: translateY(-2px);
}

/* ---------- Animations ---------- */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

.animate-fade-in-up {
    animation: fadeInUp 0.6s ease forwards;
}

.animate-fade-in {
    animation: fadeIn 0.5s ease forwards;
}

/* 分段延迟 */
.delay-1 {
    animation-delay: 0.1s;
}

.delay-2 {
    animation-delay: 0.2s;
}

.delay-3 {
    animation-delay: 0.3s;
}

.delay-4 {
    animation-delay: 0.4s;
}

.delay-5 {
    animation-delay: 0.5s;
}

/* ---------- Responsive ---------- */
@media (max-width: 1024px) {
    .chapter-sidebar {
        transform: translateX(-100%);
    }

    .chapter-sidebar.open {
        transform: translateX(0);
    }

    .chapter-content {
        margin-left: 0;
        max-width: 100%;
        padding: var(--spacing-xl) var(--spacing-lg);
    }
}

@media (max-width: 768px) {
    html {
        font-size: 15px;
    }

    .menu-toggle {
        display: flex;
    }

    .nav-links {
        position: fixed;
        top: 56px;
        left: 0;
        right: 0;
        background: var(--color-bg);
        flex-direction: column;
        padding: var(--spacing-lg);
        gap: var(--spacing-sm);
        border-bottom: 1px solid var(--color-border);
        transform: translateY(-100%);
        opacity: 0;
        transition: all var(--transition-normal);
        pointer-events: none;
    }

    .nav-links.open {
        transform: translateY(0);
        opacity: 1;
        pointer-events: all;
    }

    .hero-title {
        font-size: 2.2rem;
        letter-spacing: 2px;
    }

    .hero {
        min-height: 70vh;
        padding: var(--spacing-2xl) var(--spacing-md);
    }

    .chapter-grid {
        grid-template-columns: 1fr;
    }

    .chapter-nav {
        flex-direction: column;
    }

    .section {
        padding: var(--spacing-2xl) var(--spacing-md);
    }

    h1 {
        font-size: 1.8rem;
    }

    h2 {
        font-size: 1.4rem;
    }
}

@media (max-width: 480px) {
    html {
        font-size: 14px;
    }

    .hero-title {
        font-size: 1.8rem;
    }

    .hero-subtitle {
        font-size: 0.95rem;
    }
}

/* ---------- Utility Classes ---------- */
.text-center {
    text-align: center;
}

.text-muted {
    color: var(--color-text-muted);
}

.mt-sm {
    margin-top: var(--spacing-sm);
}

.mt-md {
    margin-top: var(--spacing-md);
}

.mt-lg {
    margin-top: var(--spacing-lg);
}

.mb-md {
    margin-bottom: var(--spacing-md);
}

.mb-lg {
    margin-bottom: var(--spacing-lg);
}

.hidden {
    display: none !important;
}