:root {
    --primary: #4f46e5;
    --primary-light: #6366f1;
    --primary-dark: #4338ca;
    --primary-50: #eef2ff;
    --primary-100: #e0e7ff;
    --primary-200: #c7d2fe;
    --secondary: #7c3aed;
    --success: #10b981;
    --success-light: #d1fae5;
    --warning: #f59e0b;
    --warning-light: #fef3c7;
    --danger: #ef4444;
    --danger-light: #fee2e2;
    --info: #3b82f6;
    --info-light: #dbeafe;

    --text-primary: #111827;
    --text-secondary: #4b5563;
    --text-muted: #9ca3af;
    --text-inverse: #ffffff;

    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --bg-card: #ffffff;

    --border: #e5e7eb;
    --border-light: #f3f4f6;

    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -1px rgba(0,0,0,0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -2px rgba(0,0,0,0.05);

    --radius-sm: 6px;
    --radius: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;

    --font-sans: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

    --header-height: 64px;
    --container-max: 1200px;
    --transition: 0.2s ease;
}

[data-theme="dark"] {
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --text-muted: #6b7280;

    --bg-primary: #111827;
    --bg-secondary: #1f2937;
    --bg-tertiary: #374151;
    --bg-card: #1f2937;

    --border: #374151;
    --border-light: #1f2937;

    --primary-50: #1e1b4b;
    --primary-100: #312e81;
    --primary-200: #3730a3;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    color: var(--text-primary);
    background: var(--bg-primary);
    line-height: 1.6;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
}

/* 隐藏滚动条但保留滚动功能 */
::-webkit-scrollbar {
    width: 0;
    height: 0;
    background: transparent;
}

* {
    scrollbar-width: none;
    -ms-overflow-style: none;
}

*::-webkit-scrollbar {
    display: none;
}

#main-content {
    transition: opacity 0.2s ease;
}

.btn {
    transition: background-color 0.15s ease, border-color 0.15s ease, box-shadow 0.15s ease;
    -webkit-tap-highlight-color: transparent;
}

.btn:active {
    filter: brightness(0.92);
}

.subject-card {
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
    -webkit-tap-highlight-color: transparent;
}

.subject-card:active {
    border-color: var(--primary);
    box-shadow: var(--shadow-md);
}

.option-item, .exam-option {
    transition: background-color 0.15s ease, border-color 0.15s ease;
    -webkit-tap-highlight-color: transparent;
}

.option-item:active, .exam-option:active {
    background: var(--primary-50);
}

.container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 24px;
}

.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--header-height);
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border);
    z-index: 100;
    backdrop-filter: blur(8px);
    background: rgba(255,255,255,0.9);
}

[data-theme="dark"] .header {
    background: rgba(17,24,39,0.9);
}

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

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    color: var(--text-primary);
    font-weight: 700;
    font-size: 18px;
}

.logo-mark {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
    border-radius: var(--radius);
    padding: 6px;
}

.logo-mark svg {
    width: 100%;
    height: 100%;
}

.nav {
    display: flex;
    gap: 8px;
}

.nav-link {
    display: inline-flex;
    align-items: center;
    padding: 8px 16px;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 14px;
    font-weight: 500;
    border-radius: var(--radius);
    transition: all var(--transition);
}

.nav-link:hover {
    color: var(--primary);
    background: var(--primary-50);
}

.nav-link.active {
    color: var(--primary);
    background: var(--primary-50);
}

.header-right {
    display: flex;
    align-items: center;
    gap: 8px;
}

.btn-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    border-radius: var(--radius);
    transition: all var(--transition);
}

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

.mobile-menu-btn {
    display: none;
    flex-direction: column;
    gap: 5px;
    padding: 8px;
    background: transparent;
    border: none;
    cursor: pointer;
}

.mobile-menu-btn span {
    display: block;
    width: 20px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: all var(--transition);
}

.mobile-menu {
    display: none;
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border);
    z-index: 99;
    padding: 16px;
}

.mobile-menu.active {
    display: block;
}

.mobile-nav {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.mobile-nav-link {
    display: block;
    padding: 12px 16px;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 15px;
    font-weight: 500;
    border-radius: var(--radius);
    transition: all var(--transition);
}

.mobile-nav-link:hover,
.mobile-nav-link.active {
    color: var(--primary);
    background: var(--primary-50);
}

main {
    margin-top: var(--header-height);
    min-height: calc(100vh - var(--header-height) - 200px);
}

.footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border);
    padding: 32px 0;
    margin-top: 64px;
}

.footer .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.footer-content {
    display: flex;
    align-items: center;
    gap: 16px;
}

.footer-brand {
    display: flex;
    align-items: center;
    gap: 8px;
    font-weight: 600;
}

.footer-desc {
    color: var(--text-muted);
    font-size: 14px;
}

.footer-links {
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 14px;
    color: var(--text-muted);
}

.footer-links a {
    color: var(--text-secondary);
    text-decoration: none;
}

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

.hero {
    padding: 80px 0 60px;
    text-align: center;
    background: linear-gradient(180deg, var(--primary-50) 0%, transparent 100%);
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 6px 16px;
    background: var(--bg-primary);
    border: 1px solid var(--border);
    border-radius: var(--radius-xl);
    font-size: 13px;
    color: var(--text-secondary);
    margin-bottom: 24px;
}

.hero-title {
    font-size: 42px;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 20px;
    letter-spacing: -0.02em;
}

.hero-subtitle {
    font-size: 18px;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto 32px;
}

.gradient-text {
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.section {
    padding: 60px 0;
}

.section-header {
    text-align: center;
    margin-bottom: 48px;
}

.section-label {
    display: inline-block;
    font-size: 13px;
    font-weight: 600;
    color: var(--primary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 8px;
}

.section-title {
    font-size: 32px;
    font-weight: 700;
    margin-bottom: 12px;
}

.section-desc {
    font-size: 16px;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 24px;
    margin-bottom: 48px;
}

.stat-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    padding: 24px;
    text-align: center;
}

.stat-number {
    font-size: 36px;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 4px;
}

.stat-label {
    font-size: 14px;
    color: var(--text-muted);
}

.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
}

.subject-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    padding: 24px;
    cursor: pointer;
    transition: all var(--transition);
    text-decoration: none;
    color: inherit;
    display: block;
}

.subject-card:hover {
    border-color: var(--primary);
    box-shadow: var(--shadow-md);
}

.subject-icon {
    width: 48px;
    height: 48px;
    background: var(--primary-50);
    border-radius: var(--radius);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 24px;
    margin-bottom: 16px;
}

.subject-name {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 8px;
}

.subject-desc {
    font-size: 14px;
    color: var(--text-muted);
    margin-bottom: 16px;
    line-height: 1.5;
}

.subject-meta {
    display: flex;
    gap: 16px;
    font-size: 13px;
    color: var(--text-secondary);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 24px;
}

.feature-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    padding: 24px;
}

.feature-icon {
    width: 40px;
    height: 40px;
    background: var(--primary-50);
    border-radius: var(--radius);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    margin-bottom: 16px;
}

.feature-title {
    font-size: 16px;
    font-weight: 600;
    margin-bottom: 8px;
}

.feature-desc {
    font-size: 14px;
    color: var(--text-muted);
    line-height: 1.5;
}

.page-header {
    padding: 32px 0;
    border-bottom: 1px solid var(--border);
    margin-bottom: 32px;
}

.breadcrumb {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    color: var(--text-muted);
    margin-bottom: 16px;
}

.breadcrumb a {
    color: var(--text-secondary);
    text-decoration: none;
}

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

.page-title {
    font-size: 28px;
    font-weight: 700;
    margin-bottom: 8px;
}

.page-desc {
    font-size: 16px;
    color: var(--text-secondary);
}

.content-layout {
    display: grid;
    grid-template-columns: 260px 1fr;
    gap: 32px;
    padding-bottom: 60px;
}

.sidebar {
    position: sticky;
    top: calc(var(--header-height) + 24px);
    max-height: calc(100vh - var(--header-height) - 48px);
    overflow-y: auto;
}

.sidebar-section {
    margin-bottom: 24px;
}

.sidebar-title {
    font-size: 12px;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    padding: 0 12px;
    margin-bottom: 8px;
}

.sidebar-nav {
    display: flex;
    flex-direction: column;
    gap: 2px;
}

.sidebar-link {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 10px 12px;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 14px;
    border-radius: var(--radius);
    transition: all var(--transition);
}

.sidebar-link:hover {
    color: var(--text-primary);
    background: var(--bg-tertiary);
}

.sidebar-link.active {
    color: var(--primary);
    background: var(--primary-50);
}

.sidebar-link .badge {
    font-size: 11px;
    padding: 2px 6px;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
}

.main-content {
    max-width: 800px;
}

@media (max-width: 768px) {
    .nav {
        display: none;
    }

    .mobile-menu-btn {
        display: flex;
    }

    .hero-title {
        font-size: 28px;
    }

    .hero-subtitle {
        font-size: 16px;
    }

    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .content-layout {
        grid-template-columns: 1fr;
    }

    .sidebar {
        position: static;
        max-height: none;
    }

    .footer .container {
        flex-direction: column;
        gap: 16px;
        text-align: center;
    }
}

/* 响应式布局优化 */
@media (max-width: 480px) {
    .container {
        padding: 0 16px;
    }

    .hero {
        padding: 48px 0 32px;
    }

    .hero-title {
        font-size: 24px;
    }

    .hero-subtitle {
        font-size: 14px;
    }

    .section {
        padding: 32px 0;
    }

    .section-title {
        font-size: 24px;
    }

    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 12px;
    }

    .stat-card {
        padding: 16px;
    }

    .stat-number {
        font-size: 28px;
    }

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

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

    .btn-lg {
        padding: 12px 20px;
        font-size: 14px;
    }

    .paper-list {
        grid-template-columns: 1fr;
    }

    .subject-tabs {
        gap: 6px;
    }

    .subject-tab {
        padding: 8px 14px;
        font-size: 13px;
    }

    .question-number {
        padding: 8px 14px;
        font-size: 13px;
    }

    .question-number-index {
        font-size: 18px;
    }

    .question-text {
        font-size: 15px;
    }

    .option-item {
        padding: 12px 14px;
    }

    .option-text {
        font-size: 14px;
    }

    .exam-topbar-inner {
        padding: 0 12px;
    }

    .question-dots {
        gap: 4px;
    }

    .question-dot {
        width: 24px;
        height: 24px;
        font-size: 11px;
    }

    .exam-bottombar-inner {
        padding: 0 12px;
    }

    .btn-nav {
        padding: 10px 16px;
        font-size: 13px;
    }
}