/* ========================================
   自助学习网站 - 主样式表
   ======================================== */

/* CSS变量定义 */
:root {
    /* 颜色系统 - 日间模式 */
    --color-primary: #6366f1;
    --color-primary-dark: #4f46e5;
    --color-primary-light: #818cf8;
    --color-secondary: #ec4899;
    --color-accent: #f59e0b;
    
    --color-bg: #ffffff;
    --color-bg-secondary: #f8fafc;
    --color-bg-tertiary: #f1f5f9;
    --color-surface: #ffffff;
    
    --color-text: #1e293b;
    --color-text-secondary: #64748b;
    --color-text-muted: #94a3b8;
    
    --color-border: #e2e8f0;
    --color-border-light: #f1f5f9;
    
    /* 学科颜色 */
    --color-science: #3b82f6;
    --color-tech: #10b981;
    --color-arts: #f59e0b;
    
    /* 阴影 */
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow: 0 1px 3px 0 rgb(0 0 0 / 0.1), 0 1px 2px -1px rgb(0 0 0 / 0.1);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
    --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);
    
    /* 动画 */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;
    
    /* 圆角 */
    --radius-sm: 0.375rem;
    --radius: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --radius-full: 9999px;
    
    /* 间距 */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.25rem;
    --space-6: 1.5rem;
    --space-8: 2rem;
    --space-10: 2.5rem;
    --space-12: 3rem;
    --space-16: 4rem;
    --space-20: 5rem;
    
    /* 字体 */
    --font-sans: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'Fira Code', Consolas, monospace;
    
    /* 头部高度 */
    --header-height: 72px;
}

/* 夜间模式变量 */
[data-theme="dark"] {
    --color-bg: #0f172a;
    --color-bg-secondary: #1e293b;
    --color-bg-tertiary: #334155;
    --color-surface: #1e293b;
    
    --color-text: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    
    --color-border: #334155;
    --color-border-light: #1e293b;
    
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.3);
    --shadow: 0 1px 3px 0 rgb(0 0 0 / 0.4), 0 1px 2px -1px rgb(0 0 0 / 0.4);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.4), 0 2px 4px -2px rgb(0 0 0 / 0.4);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.4), 0 4px 6px -4px rgb(0 0 0 / 0.4);
    --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.5), 0 8px 10px -6px rgb(0 0 0 / 0.5);
}

/* ========================================
   基础重置
   ======================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    overflow-x: hidden;
    transition: background-color var(--transition-base), color var(--transition-base);
}

img, picture, video, canvas, svg {
    display: block;
    max-width: 100%;
}

input, button, textarea, select {
    font: inherit;
}

p, h1, h2, h3, h4, h5, h6 {
    overflow-wrap: break-word;
}

a {
    color: inherit;
    text-decoration: none;
}

ul, ol {
    list-style: none;
}

button {
    cursor: pointer;
    border: none;
    background: none;
}

/* ========================================
   页面加载动画
   ======================================== */
.page-loader {
    position: fixed;
    inset: 0;
    background: var(--color-bg);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    transition: opacity 0.5s ease, visibility 0.5s ease;
}

.page-loader.hidden {
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
}

.loader-content {
    text-align: center;
}

.loader-earth {
    width: 80px;
    height: 80px;
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
    border-radius: 50%;
    position: relative;
    margin: 0 auto var(--space-6);
    box-shadow: 0 0 40px rgba(99, 102, 241, 0.4);
    animation: earthPulse 2s ease-in-out infinite;
}

@keyframes earthPulse {
    0%, 100% { transform: scale(1); box-shadow: 0 0 40px rgba(99, 102, 241, 0.4); }
    50% { transform: scale(1.05); box-shadow: 0 0 60px rgba(99, 102, 241, 0.6); }
}

.loader-orbit {
    position: absolute;
    width: 120px;
    height: 120px;
    border: 2px dashed rgba(99, 102, 241, 0.3);
    border-radius: 50%;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    animation: orbitRotate 4s linear infinite;
}

@keyframes orbitRotate {
    from { transform: translate(-50%, -50%) rotate(0deg); }
    to { transform: translate(-50%, -50%) rotate(360deg); }
}

.loader-moon {
    width: 16px;
    height: 16px;
    background: var(--color-accent);
    border-radius: 50%;
    position: absolute;
    top: -8px;
    left: 50%;
    transform: translateX(-50%);
    box-shadow: 0 0 10px var(--color-accent);
}

.loader-text {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-4);
    animation: textPulse 1.5s ease-in-out infinite;
}

@keyframes textPulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.loader-progress {
    width: 200px;
    height: 4px;
    background: var(--color-bg-tertiary);
    border-radius: var(--radius-full);
    overflow: hidden;
    margin: 0 auto var(--space-2);
}

.loader-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--color-primary), var(--color-secondary));
    border-radius: var(--radius-full);
    width: 0%;
    transition: width 0.3s ease;
}

.loader-percent {
    font-size: 0.875rem;
    color: var(--color-text-muted);
    font-variant-numeric: tabular-nums;
}

/* 页面切换过渡 */
.page-transition {
    position: fixed;
    inset: 0;
    background: var(--color-bg);
    z-index: 9998;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s ease;
}

.page-transition.active {
    opacity: 1;
    visibility: visible;
}

/* ========================================
   导航栏样式
   ======================================== */
.main-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--header-height);
    z-index: 1000;
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--color-border-light);
    transition: all var(--transition-base);
}

[data-theme="dark"] .main-header {
    background: rgba(15, 23, 42, 0.8);
}

.main-header.scrolled {
    height: 64px;
    box-shadow: var(--shadow-md);
}

.main-nav {
    height: 100%;
}

.nav-container {
    max-width: 1400px;
    height: 100%;
    margin: 0 auto;
    padding: 0 var(--space-6);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

/* Logo样式 */
.logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    transition: transform var(--transition-fast);
}

.logo:hover {
    transform: scale(1.02);
}

.logo-icon-wrapper {
    position: relative;
    width: 44px;
    height: 44px;
}

.logo-icon {
    font-size: 1.75rem;
    display: block;
    animation: iconFloat 3s ease-in-out infinite;
}

@keyframes iconFloat {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-3px); }
}

.logo-particles {
    position: absolute;
    inset: -8px;
    pointer-events: none;
}

.logo-text-wrapper {
    display: flex;
    flex-direction: column;
}

.logo-text {
    font-size: 1.25rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    line-height: 1.2;
}

.logo-tagline {
    font-size: 0.75rem;
    color: var(--color-text-muted);
}

/* 导航菜单 */
.nav-menu {
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.nav-link {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-2) var(--space-4);
    border-radius: var(--radius-md);
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
    position: relative;
}

.nav-link:hover,
.nav-link.active {
    color: var(--color-primary);
    background: rgba(99, 102, 241, 0.1);
}

.nav-icon {
    font-size: 1.125rem;
}

/* 下拉菜单 */
.dropdown {
    position: relative;
}

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

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

.dropdown-menu {
    position: absolute;
    top: 100%;
    left: 50%;
    transform: translateX(-50%) translateY(10px);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-xl);
    padding: var(--space-4);
    min-width: 600px;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-fast);
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-6);
}

.dropdown:hover .dropdown-menu {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) translateY(0);
}

.mega-menu-category .category-title {
    display: block;
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--space-3);
    padding-bottom: var(--space-2);
    border-bottom: 1px solid var(--color-border);
}

.category-items li {
    margin-bottom: var(--space-2);
}

.category-items a {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-2);
    border-radius: var(--radius);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.category-items a:hover {
    background: var(--color-bg-tertiary);
    color: var(--color-primary);
}

.subject-emoji {
    font-size: 1rem;
}

/* 导航操作区 */
.nav-actions {
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.action-btn {
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-md);
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.action-btn:hover {
    background: var(--color-bg-tertiary);
    color: var(--color-primary);
}

.action-btn .icon {
    width: 20px;
    height: 20px;
}

/* 进度小组件 */
.progress-widget {
    position: relative;
    cursor: pointer;
}

.progress-ring {
    width: 40px;
    height: 40px;
    position: relative;
}

.progress-ring svg {
    width: 100%;
    height: 100%;
    transform: rotate(-90deg);
}

.progress-ring-bg {
    fill: none;
    stroke: var(--color-bg-tertiary);
    stroke-width: 3;
}

.progress-ring-fill {
    fill: none;
    stroke: var(--color-primary);
    stroke-width: 3;
    stroke-linecap: round;
    transition: stroke-dasharray var(--transition-slow);
}

.progress-text {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 0.625rem;
    font-weight: 700;
    color: var(--color-primary);
}

/* 主题切换 */
.theme-toggle {
    position: relative;
    overflow: hidden;
}

.theme-icon {
    position: absolute;
    transition: all var(--transition-base);
}

.theme-icon.light {
    opacity: 1;
    transform: translateY(0) rotate(0);
}

.theme-icon.dark {
    opacity: 0;
    transform: translateY(20px) rotate(-90deg);
}

[data-theme="dark"] .theme-icon.light {
    opacity: 0;
    transform: translateY(-20px) rotate(90deg);
}

[data-theme="dark"] .theme-icon.dark {
    opacity: 1;
    transform: translateY(0) rotate(0);
}

/* 移动端菜单按钮 */
.mobile-toggle {
    display: none;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    width: 40px;
    height: 40px;
    gap: 5px;
}

.hamburger-line {
    width: 22px;
    height: 2px;
    background: var(--color-text);
    border-radius: 2px;
    transition: all var(--transition-fast);
}

.mobile-toggle.active .hamburger-line:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.mobile-toggle.active .hamburger-line:nth-child(2) {
    opacity: 0;
}

.mobile-toggle.active .hamburger-line:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

/* ========================================
   搜索弹窗
   ======================================== */
.search-modal {
    position: fixed;
    inset: 0;
    z-index: 2000;
    display: flex;
    align-items: flex-start;
    justify-content: center;
    padding-top: 10vh;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-base);
}

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

.search-overlay {
    position: absolute;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
}

.search-container {
    position: relative;
    width: 90%;
    max-width: 700px;
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-xl);
    overflow: hidden;
    transform: translateY(-20px);
    transition: transform var(--transition-base);
}

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

.search-header {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    padding: var(--space-4);
    border-bottom: 1px solid var(--color-border);
}

.search-input-wrapper {
    flex: 1;
    display: flex;
    align-items: center;
    gap: var(--space-3);
    background: var(--color-bg-tertiary);
    border-radius: var(--radius-lg);
    padding: 0 var(--space-4);
}

.search-icon {
    width: 20px;
    height: 20px;
    color: var(--color-text-muted);
    flex-shrink: 0;
}

.search-input {
    flex: 1;
    padding: var(--space-3) 0;
    background: transparent;
    border: none;
    color: var(--color-text);
    font-size: 1rem;
}

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

.search-input:focus {
    outline: none;
}

.search-clear {
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-full);
    background: var(--color-border);
    color: var(--color-text-secondary);
    font-size: 0.75rem;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-fast);
}

.search-input:not(:placeholder-shown) + .search-clear {
    opacity: 1;
    visibility: visible;
}

.search-close {
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-md);
    color: var(--color-text-secondary);
    font-size: 1.25rem;
    transition: all var(--transition-fast);
}

.search-close:hover {
    background: var(--color-bg-tertiary);
    color: var(--color-text);
}

.search-results {
    max-height: 400px;
    overflow-y: auto;
    padding: var(--space-4);
}

.search-suggestions h4 {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-3);
}

.suggestion-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-2);
}

.tag {
    padding: var(--space-2) var(--space-3);
    background: var(--color-bg-tertiary);
    border-radius: var(--radius-full);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.tag:hover {
    background: var(--color-primary);
    color: white;
}

/* ========================================
   Hero区域
   ======================================== */
.hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: calc(var(--header-height) + var(--space-12)) var(--space-6) var(--space-12);
    overflow: hidden;
}

/* 3D背景容器 */
.hero-3d-bg {
    position: absolute;
    inset: 0;
    z-index: 0;
}

.hero-3d-bg canvas {
    width: 100% !important;
    height: 100% !important;
}

/* 粒子画布 */
.hero-particles {
    position: absolute;
    inset: 0;
    z-index: 1;
    pointer-events: none;
}

/* 涟漪效果层 */
.hero-ripple {
    position: absolute;
    inset: 0;
    z-index: 2;
    pointer-events: none;
}

.ripple {
    position: absolute;
    border-radius: 50%;
    background: radial-gradient(circle, rgba(99, 102, 241, 0.3) 0%, transparent 70%);
    transform: scale(0);
    animation: rippleEffect 1s ease-out forwards;
}

@keyframes rippleEffect {
    to {
        transform: scale(4);
        opacity: 0;
    }
}

/* Hero内容 */
.hero-content {
    position: relative;
    z-index: 3;
    max-width: 900px;
    text-align: center;
}

/* 面包屑导航 */
.breadcrumb {
    margin-bottom: var(--space-6);
}

.breadcrumb ol {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: var(--space-2);
    font-size: 0.875rem;
    color: var(--color-text-muted);
}

.breadcrumb .current {
    color: var(--color-primary);
    font-weight: 500;
}

/* Hero标题 */
.hero-title {
    margin-bottom: var(--space-6);
}

.title-line {
    display: block;
    font-size: clamp(2.5rem, 6vw, 4.5rem);
    font-weight: 900;
    line-height: 1.1;
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 50%, var(--color-accent) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    animation: titleReveal 1s ease-out;
}

@keyframes titleReveal {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.title-line-sub {
    font-size: clamp(1.5rem, 3vw, 2.5rem);
    font-weight: 300;
    color: var(--color-text-secondary);
    -webkit-text-fill-color: var(--color-text-secondary);
    margin-top: var(--space-3);
    animation: titleReveal 1s ease-out 0.2s both;
}

.hero-desc {
    font-size: clamp(1rem, 1.5vw, 1.25rem);
    color: var(--color-text-secondary);
    max-width: 600px;
    margin: 0 auto var(--space-8);
    line-height: 1.8;
    animation: titleReveal 1s ease-out 0.3s both;
}

.hero-desc strong {
    color: var(--color-primary);
}

/* Hero搜索框 */
.hero-search {
    margin-bottom: var(--space-12);
    animation: titleReveal 1s ease-out 0.4s both;
}

.hero-search-box {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    background: var(--color-surface);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-xl);
    padding: var(--space-2);
    max-width: 560px;
    margin: 0 auto;
    box-shadow: var(--shadow-lg);
    transition: all var(--transition-fast);
}

.hero-search-box:focus-within {
    border-color: var(--color-primary);
    box-shadow: var(--shadow-glow);
}

.hero-search-box .search-icon {
    margin-left: var(--space-3);
}

.hero-search-box input {
    flex: 1;
    padding: var(--space-3);
    border: none;
    background: transparent;
    color: var(--color-text);
    font-size: 1rem;
}

.hero-search-box input:focus {
    outline: none;
}

.hero-search-box .btn {
    padding: var(--space-3) var(--space-6);
    font-weight: 600;
}

.search-hot {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-3);
    margin-top: var(--space-4);
    font-size: 0.875rem;
    color: var(--color-text-muted);
    flex-wrap: wrap;
}

.search-hot a {
    color: var(--color-text-secondary);
    transition: color var(--transition-fast);
}

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

/* 数据统计 */
.hero-stats {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--space-6);
    max-width: 800px;
    margin: 0 auto;
    animation: titleReveal 1s ease-out 0.5s both;
}

.stat-item {
    text-align: center;
    padding: var(--space-6);
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    border: 1px solid var(--color-border);
    box-shadow: var(--shadow);
    transition: all var(--transition-fast);
}

.stat-item:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.stat-number {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 2px;
    font-size: 2rem;
    font-weight: 900;
    color: var(--color-primary);
    line-height: 1;
    margin-bottom: var(--space-2);
}

.counter {
    font-variant-numeric: tabular-nums;
}

.stat-suffix {
    font-size: 1.25rem;
    font-weight: 700;
}

.stat-label {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-3);
}

.stat-icon {
    font-size: 1.5rem;
}

/* 滚动指示器 */
.scroll-indicator {
    position: absolute;
    bottom: var(--space-8);
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--space-3);
    animation: bounce 2s ease-in-out infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateX(-50%) translateY(0); }
    50% { transform: translateX(-50%) translateY(10px); }
}

.scroll-mouse {
    width: 26px;
    height: 40px;
    border: 2px solid var(--color-text-muted);
    border-radius: var(--radius-full);
    display: flex;
    justify-content: center;
    padding-top: var(--space-2);
}

.scroll-wheel {
    width: 4px;
    height: 8px;
    background: var(--color-text-muted);
    border-radius: var(--radius-full);
    animation: scrollWheel 1.5s ease-in-out infinite;
}

@keyframes scrollWheel {
    0%, 100% { transform: translateY(0); opacity: 1; }
    50% { transform: translateY(8px); opacity: 0.3; }
}

.scroll-text {
    font-size: 0.75rem;
    color: var(--color-text-muted);
}

/* ========================================
   通用容器和区块
   ======================================== */
.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 var(--space-6);
}

.section-header {
    text-align: center;
    margin-bottom: var(--space-12);
}

.section-tag {
    display: inline-block;
    padding: var(--space-2) var(--space-4);
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.1), rgba(236, 72, 153, 0.1));
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-primary);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    margin-bottom: var(--space-4);
}

.section-title {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 800;
    color: var(--color-text);
    margin-bottom: var(--space-4);
}

.section-desc {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    max-width: 600px;
    margin: 0 auto;
}

/* ========================================
   学科区块
   ======================================== */
.subjects-section {
    padding: var(--space-20) 0;
    background: var(--color-bg-secondary);
}

/* 筛选标签 */
.filter-tabs {
    display: flex;
    justify-content: center;
    gap: var(--space-3);
    margin-bottom: var(--space-10);
    flex-wrap: wrap;
}

.filter-btn {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-5);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-full);
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.filter-btn:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

.filter-btn.active {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: white;
    box-shadow: var(--shadow-glow);
}

.filter-count {
    padding: 2px 8px;
    background: rgba(0, 0, 0, 0.1);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
}

.filter-btn.active .filter-count {
    background: rgba(255, 255, 255, 0.2);
}

/* 3D卡片网格 */
.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: var(--space-6);
    perspective: 1000px;
}

.subject-card-3d {
    height: 380px;
    perspective: 1000px;
    cursor: pointer;
}

.card-3d-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

.subject-card-3d:hover .card-3d-inner {
    transform: rotateY(180deg);
}

.card-3d-front,
.card-3d-back {
    position: absolute;
    inset: 0;
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    border: 1px solid var(--color-border);
    padding: var(--space-8);
    backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    box-shadow: var(--shadow);
    transition: box-shadow var(--transition-fast);
}

.subject-card-3d:hover .card-3d-front {
    box-shadow: var(--shadow-xl);
}

.card-3d-back {
    transform: rotateY(180deg);
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    color: white;
    border-color: transparent;
}

.subject-icon-3d {
    width: 80px;
    height: 80px;
    margin-bottom: var(--space-6);
    position: relative;
}

.icon-scene {
    position: absolute;
    inset: 0;
}

.icon-emoji {
    font-size: 4rem;
    display: block;
    animation: iconFloat 3s ease-in-out infinite;
}

.subject-name {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--space-3);
}

.card-3d-back .subject-name {
    color: white;
}

.subject-desc {
    font-size: 0.9375rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    flex: 1;
}

.subject-meta {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: var(--space-4);
    padding-top: var(--space-4);
    border-top: 1px solid var(--color-border);
    font-size: 0.875rem;
    color: var(--color-text-muted);
}

.course-count {
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.course-count svg {
    width: 16px;
    height: 16px;
}

/* 卡片背面内容 */
.card-3d-back h4 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--space-4);
}

.path-preview {
    flex: 1;
}

.path-preview li {
    padding: var(--space-2) 0;
    font-size: 0.9375rem;
    opacity: 0.9;
}

.card-3d-back .btn {
    margin-top: auto;
    background: white;
    color: var(--color-primary);
}

.card-3d-back .btn:hover {
    background: rgba(255, 255, 255, 0.9);
}

/* ========================================
   推荐内容区块
   ======================================== */
.recommended-section {
    padding: var(--space-20) 0;
}

.recommended-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--space-6);
}

.recommended-card {
    position: relative;
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    overflow: hidden;
    border: 1px solid var(--color-border);
    box-shadow: var(--shadow);
    transition: all var(--transition-fast);
}

.recommended-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
}

.recommended-card.featured {
    grid-column: span 2;
    grid-row: span 2;
}

.card-image {
    position: relative;
    height: 160px;
    overflow: hidden;
}

.recommended-card.featured .card-image {
    height: 280px;
}

.image-gradient {
    position: absolute;
    inset: 0;
}

.card-badge {
    position: absolute;
    top: var(--space-3);
    left: var(--space-3);
    padding: var(--space-1) var(--space-3);
    background: rgba(255, 255, 255, 0.9);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-text);
}

.card-badge.hot {
    background: linear-gradient(135deg, #ff6b6b, #ee5a6f);
    color: white;
}

.card-badge.new {
    background: linear-gradient(135deg, #4ecdc4, #44a08d);
    color: white;
}

.card-category {
    position: absolute;
    top: var(--space-3);
    right: var(--space-3);
    padding: var(--space-1) var(--space-3);
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 500;
    color: white;
}

.card-content {
    padding: var(--space-5);
}

.card-content h3 {
    font-size: 1.125rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--space-2);
}

.recommended-card.featured .card-content h3 {
    font-size: 1.5rem;
}

.card-content p {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-bottom: var(--space-4);
}

.card-meta {
    display: flex;
    align-items: center;
    gap: var(--space-4);
    margin-bottom: var(--space-3);
}

.meta-item {
    display: flex;
    align-items: center;
    gap: var(--space-1);
    font-size: 0.75rem;
    color: var(--color-text-muted);
}

.meta-item svg {
    width: 14px;
    height: 14px;
}

.card-rating {
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.stars {
    font-size: 0.875rem;
}

.score {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-accent);
}

.card-link {
    position: absolute;
    inset: 0;
    z-index: 1;
}

/* ========================================
   学习路径区块
   ======================================== */
.pathway-section {
    padding: var(--space-20) 0;
    background: var(--color-bg-secondary);
}

.pathway-visual {
    position: relative;
    max-width: 1000px;
    margin: 0 auto var(--space-12);
}

.pathway-line {
    position: absolute;
    top: 40px;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--color-border);
    border-radius: var(--radius-full);
}

.pathway-line::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
    width: 0%;
    background: linear-gradient(90deg, var(--color-primary), var(--color-secondary));
    border-radius: var(--radius-full);
    transition: width 1.5s ease;
}

.pathway-line.animate::after {
    width: 100%;
}

.pathway-nodes {
    display: flex;
    justify-content: space-between;
    position: relative;
}

.pathway-node {
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    width: 200px;
}

.node-icon {
    position: relative;
    width: 80px;
    height: 80px;
    background: var(--color-surface);
    border: 3px solid var(--color-border);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    margin-bottom: var(--space-4);
    z-index: 1;
    transition: all var(--transition-fast);
}

.pathway-node:hover .node-icon {
    border-color: var(--color-primary);
    box-shadow: var(--shadow-glow);
    transform: scale(1.1);
}

.node-pulse {
    position: absolute;
    inset: -5px;
    border-radius: 50%;
    border: 2px solid var(--color-primary);
    opacity: 0;
    animation: nodePulse 2s ease-out infinite;
}

@keyframes nodePulse {
    0% { transform: scale(1); opacity: 1; }
    100% { transform: scale(1.3); opacity: 0; }
}

.node-content h4 {
    font-size: 1.125rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--space-2);
}

.node-content p {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-3);
}

.node-courses {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: var(--space-2);
}

.course-tag {
    padding: var(--space-1) var(--space-3);
    background: var(--color-bg-tertiary);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    color: var(--color-text-secondary);
}

.pathway-cta {
    text-align: center;
}

.cta-hint {
    margin-top: var(--space-4);
    font-size: 0.9375rem;
    color: var(--color-text-muted);
}

.cta-hint strong {
    color: var(--color-primary);
}

/* ========================================
   按钮样式
   ======================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-6);
    border-radius: var(--radius-lg);
    font-size: 0.9375rem;
    font-weight: 600;
    transition: all var(--transition-fast);
    border: none;
    cursor: pointer;
}

.btn-primary {
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    color: white;
    box-shadow: 0 4px 15px rgba(99, 102, 241, 0.4);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.5);
}

.btn-outline {
    background: transparent;
    color: var(--color-text);
    border: 2px solid var(--color-border);
}

.btn-outline:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

.btn-lg {
    padding: var(--space-4) var(--space-8);
    font-size: 1rem;
}

/* ========================================
   页脚
   ======================================== */
.main-footer {
    padding: var(--space-16) 0 var(--space-8);
    background: var(--color-bg-tertiary);
    border-top: 1px solid var(--color-border);
}

.footer-container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 var(--space-6);
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr repeat(4, 1fr);
    gap: var(--space-10);
    margin-bottom: var(--space-12);
}

.footer-brand {
    max-width: 300px;
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--space-4);
}

.footer-desc {
    font-size: 0.9375rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-bottom: var(--space-6);
}

.footer-social {
    display: flex;
    gap: var(--space-3);
}

.social-link {
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--color-surface);
    border-radius: var(--radius-md);
    color: var(--color-text-muted);
    transition: all var(--transition-fast);
}

.social-link svg {
    width: 20px;
    height: 20px;
}

.social-link:hover {
    background: var(--color-primary);
    color: white;
    transform: translateY(-3px);
}

.footer-links h4 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--space-4);
}

.footer-links li {
    margin-bottom: var(--space-3);
}

.footer-links a {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    transition: color var(--transition-fast);
}

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

.footer-bottom {
    text-align: center;
    padding-top: var(--space-8);
    border-top: 1px solid var(--color-border);
}

.footer-bottom p {
    font-size: 0.875rem;
    color: var(--color-text-muted);
    margin-bottom: var(--space-2);
}

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

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

.beian-divider {
    margin: 0 var(--space-2);
}

/* ========================================
   回到顶部按钮
   ======================================== */
.back-to-top {
    position: fixed;
    bottom: var(--space-6);
    right: var(--space-6);
    width: 48px;
    height: 48px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 50%;
    color: var(--color-text-secondary);
    box-shadow: var(--shadow-lg);
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all var(--transition-fast);
    z-index: 100;
}

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

.back-to-top:hover {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: white;
    transform: translateY(-3px);
}

.back-to-top svg {
    width: 20px;
    height: 20px;
}

/* ========================================
   响应式设计
   ======================================== */
@media (max-width: 1200px) {
    .recommended-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .recommended-card.featured {
        grid-column: span 2;
        grid-row: span 1;
    }
    
    .footer-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (max-width: 992px) {
    .nav-menu {
        display: none;
    }
    
    .mobile-toggle {
        display: flex;
    }
    
    .mega-menu {
        min-width: auto;
        width: 100%;
    }
    
    .hero-stats {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .subjects-grid {
        grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    }
    
    .pathway-nodes {
        flex-wrap: wrap;
        gap: var(--space-8);
        justify-content: center;
    }
    
    .pathway-line {
        display: none;
    }
    
    .pathway-node {
        width: calc(50% - var(--space-4));
    }
    
    .footer-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    :root {
        --header-height: 64px;
    }
    
    .nav-container {
        padding: 0 var(--space-4);
    }
    
    .logo-text-wrapper {
        display: none;
    }
    
    .progress-widget {
        display: none;
    }
    
    .hero {
        padding-top: calc(var(--header-height) + var(--space-8));
    }
    
    .hero-search-box {
        flex-direction: column;
        padding: var(--space-3);
    }
    
    .hero-search-box .btn {
        width: 100%;
    }
    
    .search-hot {
        display: none;
    }
    
    .subjects-grid {
        grid-template-columns: 1fr;
    }
    
    .recommended-grid {
        grid-template-columns: 1fr;
    }
    
    .recommended-card.featured {
        grid-column: span 1;
    }
    
    .card-image,
    .recommended-card.featured .card-image {
        height: 180px;
    }
    
    .filter-tabs {
        justify-content: flex-start;
        overflow-x: auto;
        padding-bottom: var(--space-2);
        -webkit-overflow-scrolling: touch;
    }
    
    .filter-btn {
        white-space: nowrap;
    }
    
    .pathway-node {
        width: 100%;
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
        gap: var(--space-8);
    }
    
    .footer-brand {
        max-width: 100%;
        text-align: center;
    }
    
    .footer-social {
        justify-content: center;
    }
}

@media (max-width: 480px) {
    .hero-stats {
        grid-template-columns: 1fr;
    }
    
    .stat-item {
        display: flex;
        align-items: center;
        gap: var(--space-4);
        text-align: left;
    }
    
    .stat-number {
        margin-bottom: 0;
    }
    
    .stat-label {
        margin-bottom: 0;
        margin-right: auto;
    }
}

/* ========================================
   减少动画偏好
   ======================================== */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
    
    html {
        scroll-behavior: auto;
    }
}

/* ========================================
   打印样式
   ======================================== */
@media print {
    .main-header,
    .hero-3d-bg,
    .hero-particles,
    .scroll-indicator,
    .back-to-top,
    .page-loader {
        display: none !important;
    }
    
    .hero {
        min-height: auto;
        padding-top: var(--space-8);
    }
    
    .subject-card-3d {
        break-inside: avoid;
    }
}

/* ========================================
   滚动条样式
   ======================================== */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--color-bg-tertiary);
}

::-webkit-scrollbar-thumb {
    background: var(--color-text-muted);
    border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--color-text-secondary);
}

/* 隐藏元素 */
.hidden {
    display: none !important;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* 筛选隐藏 */
.subject-card-3d.hidden {
    display: none;
}