/* Design tokens */
:root {
    --bg-primary: #0a0a0a;
    --bg-elevated: #111111;
    --bg-panel: #141414;
    --border-subtle: #242424;
    --border-strong: #2f2f2f;
    --text-primary: #f5f7f7;
    --text-secondary: #ccd0d0;
    --text-muted: #8e9495;
    --accent: #00d4aa;
    --accent-soft: rgba(0, 212, 170, 0.12);
    --radius-sm: 6px;
    --radius-md: 12px;
    --radius-lg: 20px;
    --shadow-soft: 0 12px 25px rgba(0, 212, 170, 0.15);
    --shadow-strong: 0 20px 40px rgba(0, 212, 170, 0.18);
}

/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 16px;
    line-height: 1.6;
    scroll-behavior: smooth;
}

body {
    font-family: "Inter", "SF Pro Text", "Segoe UI", "Noto Sans", "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-secondary);
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
}

html[lang="zh"] body {
    font-family: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", "Source Han Sans", sans-serif;
    line-height: 1.85;
}

html[lang="en"] body {
    font-family: "Inter", "Segoe UI", "Helvetica Neue", Arial, sans-serif;
}

main,
.main-content,
.page-content {
    position: relative;
}

main {
    padding-top: 2rem;
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    color: var(--text-primary);
    font-weight: 600;
    line-height: 1.2;
    margin-bottom: 1rem;
    text-wrap: balance;
}

h1 { font-size: 2.5rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }

p {
    margin-bottom: 1.25rem;
    color: var(--text-secondary);
}

strong {
    color: var(--text-primary);
    font-weight: 650;
}

em {
    font-style: italic;
}

a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.3s ease, box-shadow 0.3s ease;
}

a:hover {
    color: #00f5d4;
}

a:focus-visible,
.btn:focus-visible,
.language-switcher:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 3px;
}

/* Lists */
.page-content ul,
.page-content ol {
    margin: 0 0 1.75rem 1.5rem;
    line-height: 1.7;
}

.page-content li {
    padding-left: 0.25rem;
}

.page-content li + li {
    margin-top: 0.35rem;
}

/* Media */
.page-content img,
.page-content video,
.page-content iframe {
    max-width: 100%;
    border-radius: var(--radius-md);
    margin: 2rem 0;
    display: block;
}

.page-content figure {
    margin: 2.25rem 0;
    text-align: center;
}

.page-content figcaption {
    margin-top: 0.75rem;
    font-size: 0.9rem;
    color: var(--text-muted);
}

.page-content hr {
    border: none;
    height: 1px;
    background: var(--border-subtle);
    margin: 3rem 0;
}

/* Header */
.site-header {
    background-color: rgba(10, 10, 10, 0.92);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-subtle);
    padding: 0.75rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1.5rem;
}

.logo {
    font-size: 1.5rem;
    font-weight: bold;
}

.logo-text {
    background: linear-gradient(45deg, #00d4aa, #00f5d4);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.logo-image {
    height: 1.5rem;
    width: auto;
    vertical-align: middle;
}

.main-nav {
    display: flex;
    gap: 1.5rem;
}

.nav-link {
    color: var(--text-secondary);
    transition: color 0.3s ease;
    font-size: 0.95rem;
    letter-spacing: 0.02em;
}

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

.header-actions {
    display: flex;
    align-items: center;
}

.language-switcher {
    background: linear-gradient(45deg, #00d4aa, #00f5d4);
    color: #0a0a0a;
    border: none;
    padding: 0.55rem 1.1rem;
    border-radius: 24px;
    cursor: pointer;
    font-weight: 600;
    transition: transform 0.2s ease;
    box-shadow: var(--shadow-soft);
}

.language-switcher:hover {
    transform: translateY(-1px);
}

/* Home page */
.home-container {
    min-height: 100vh;
}

.hero-section {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 70vh;
    text-align: center;
    background: linear-gradient(135deg, #0a0a0a 0%, #151515 100%);
    padding: 5rem 0 3rem;
}

.hero-content {
    max-width: 760px;
    padding: 2.5rem 2rem;
}

.hero-content h1 {
    font-size: 3rem;
    margin-bottom: 1rem;
    background: linear-gradient(45deg, #00d4aa, #00f5d4, #00d4aa);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    animation: gradientShift 6s ease-in-out infinite;
}

@keyframes gradientShift {
    0%, 100% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
}

.subtitle {
    font-size: 1.15rem;
    color: var(--text-secondary);
    margin-bottom: 1.75rem;
}

.hero-description {
    font-size: 1.05rem;
    line-height: 1.85;
    margin-bottom: 2.5rem;
    color: var(--text-secondary);
}

.hero-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

.btn {
    display: inline-block;
    padding: 0.75rem 1.6rem;
    border-radius: 28px;
    font-weight: 600;
    text-decoration: none;
    transition: all 0.3s ease;
    cursor: pointer;
    border: none;
    box-shadow: var(--shadow-soft);
}

.btn-primary {
    background: linear-gradient(45deg, #00d4aa, #00f5d4);
    color: #0a0a0a;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-strong);
}

/* Table of Contents */
.toc-section {
    padding: 4.5rem 0;
    background-color: var(--bg-elevated);
}

.toc-container {
    max-width: 1080px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

.toc-section h2 {
    text-align: center;
    margin-bottom: 3rem;
    color: var(--text-primary);
}

.toc-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.toc-item {
    background-color: rgba(255, 255, 255, 0.05);
    border-radius: 12px;
    padding: 2rem;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid var(--border-subtle);
    backdrop-filter: blur(4px);
}

.toc-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 18px 40px rgba(0, 212, 170, 0.12);
}

.toc-number {
    display: inline-block;
    background: linear-gradient(45deg, #00d4aa, #00f5d4);
    color: #0a0a0a;
    width: 2rem;
    height: 2rem;
    border-radius: 50%;
    text-align: center;
    line-height: 2rem;
    font-weight: bold;
    margin-bottom: 1rem;
}

.toc-item h3 {
    margin-bottom: 0.5rem;
}

.toc-item h3 a {
    color: var(--text-primary);
}

.toc-item p {
    color: var(--text-muted);
    font-size: 0.95rem;
    line-height: 1.6;
}

/* Page content */
.page {
    padding: 2.5rem 0;
}

.page-header {
    text-align: center;
    margin-bottom: 3rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--border-subtle);
}

.page-title {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
}

.page-subtitle {
    font-size: 1.25rem;
    color: var(--text-muted);
}

.page-content {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 1rem;
}

.page-content h2 {
    margin-top: 2.25rem;
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-subtle);
}

.page-content h3 {
    margin-top: 1.5rem;
    margin-bottom: 0.75rem;
}

.page-content p {
    margin-bottom: 1.6rem;
    line-height: 1.85;
}

.page-content blockquote {
    border-left: 4px solid var(--accent);
    padding: 1rem 1.25rem;
    margin: 1.75rem 0;
    color: var(--text-secondary);
    font-style: italic;
    background: rgba(0, 212, 170, 0.04);
    border-radius: 0 10px 10px 0;
}

/* Code blocks */
.page-content pre {
    background-color: var(--bg-panel);
    border: 1px solid var(--border-subtle);
    border-radius: 10px;
    padding: 1.25rem;
    margin: 1.75rem 0;
    overflow-x: auto;
    font-size: 0.95rem;
}

.page-content code {
    background-color: var(--bg-panel);
    color: var(--accent);
    padding: 0.2rem 0.45rem;
    border-radius: var(--radius-sm);
    font-family: "JetBrains Mono", "Source Code Pro", Menlo, Consolas, monospace;
}

.page-content pre code {
    background: none;
    padding: 0;
}

/* Tables */
.page-content table {
    width: 100%;
    border-collapse: collapse;
    margin: 2rem 0;
    background: var(--bg-panel);
    border: 1px solid var(--border-subtle);
    border-radius: 10px;
    overflow: hidden;
}

.page-content th,
.page-content td {
    padding: 0.9rem 1rem;
    border-bottom: 1px solid var(--border-subtle);
    text-align: left;
    color: var(--text-secondary);
}

.page-content th {
    background: rgba(0, 212, 170, 0.08);
    color: var(--text-primary);
    font-weight: 600;
}

.page-content tr:last-child td {
    border-bottom: none;
}

/* Chapter navigation */
.chapter-navigation {
    display: flex;
    justify-content: space-between;
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border-subtle);
    gap: 1rem;
}

.chapter-navigation .nav-link {
    padding: 0.75rem 1.5rem;
    background-color: rgba(255, 255, 255, 0.06);
    border-radius: 10px;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 0.6rem;
}

.chapter-navigation .nav-link:hover {
    background-color: var(--accent-soft);
    transform: translateY(-2px);
}

/* Footer */
.site-footer {
    background-color: #0b0b0b;
    border-top: 1px solid var(--border-subtle);
    padding: 2rem 0;
    margin-top: 4rem;
}

.footer-container {
    text-align: center;
}

.footer-content p {
    color: var(--text-muted);
    margin-bottom: 0.5rem;
}

.footer-content a {
    color: var(--accent);
}

/* MathJax styling */
.MathJax {
    color: var(--text-primary) !important;
}

/* Custom scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: #1a1a1a;
}

::-webkit-scrollbar-thumb {
    background: var(--accent);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: #00f5d4;
}

/* Responsive design */
@media (max-width: 1024px) {
    html {
        font-size: 15.5px;
    }

    .container {
        padding: 0 1.25rem;
    }
}

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

    .header-container {
        flex-direction: column;
        gap: 1rem;
        align-items: stretch;
    }

    .main-nav {
        justify-content: center;
        gap: 1.25rem;
    }

    .hero-content h1 {
        font-size: 2.3rem;
    }

    .hero-content {
        padding: 2rem 1.25rem;
    }

    .subtitle {
        font-size: 1.05rem;
    }

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

    .page-content {
        padding: 0 0.5rem;
    }

    .chapter-navigation {
        flex-direction: column;
        align-items: stretch;
    }

    .hero-actions {
        flex-direction: column;
        align-items: center;
    }

    .toc-item {
        padding: 1.75rem;
    }
}

@media (min-width: 1200px) {
    .page-content {
        max-width: 860px;
    }
}