/* ==========================================================================
   ARENA - Main Stylesheet
   ========================================================================== */

/* --------------------------------------------------------------------------
   CSS Variables & Theming
   -------------------------------------------------------------------------- */

:root {
    /* Typography */
    --font-heading: 'Montserrat', sans-serif;
    --font-body: 'Inter', sans-serif;
    --font-mono: 'Fira Code', 'Consolas', monospace;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;

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

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;

    /* Layout */
    --nav-height: 64px;
    --sidebar-width: 280px;
    --right-sidebar-width: 300px;
    --content-max-width: 800px;
}

/* Light Theme (default) */
[data-theme="light"] {
    --color-bg: #ffffff;
    --color-bg-secondary: #f8fafc;
    --color-bg-tertiary: #f1f5f9;
    --color-surface: #ffffff;
    --color-surface-hover: #f8fafc;
    --color-border: #e2e8f0;
    --color-border-light: #f1f5f9;

    --color-text: #1e293b;
    --color-text-secondary: #64748b;
    --color-text-muted: #94a3b8;

    --color-primary: #3b82f6;
    --color-primary-hover: #2563eb;

    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --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);
}

/* Dark Theme - Greyscale */
[data-theme="dark"] {
    --color-bg: #111111;
    --color-bg-secondary: #1a1a1a;
    --color-bg-tertiary: #2a2a2a;
    --color-surface: #1a1a1a;
    --color-surface-hover: #2a2a2a;
    --color-border: #333333;
    --color-border-light: #1a1a1a;

    --color-text: #f5f5f5;
    --color-text-secondary: #a0a0a0;
    --color-text-muted: #707070;

    --color-primary: #e0e0e0;
    --color-primary-hover: #ffffff;

    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.5), 0 2px 4px -1px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5), 0 4px 6px -2px rgba(0, 0, 0, 0.4);
}

/* --------------------------------------------------------------------------
   Reset & Base Styles
   -------------------------------------------------------------------------- */

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

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

body {
    font-family: var(--font-body);
    font-size: 1rem;
    line-height: 1.6;
    color: var(--color-text);
    background-color: var(--color-bg);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

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

/* --------------------------------------------------------------------------
   Top Navigation
   -------------------------------------------------------------------------- */

.top-nav {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    height: var(--nav-height);
}

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

.nav-logo {
    display: flex;
    align-items: center;
    transition: opacity var(--transition-fast);
    padding: 0;
    margin: 0;
}

.nav-logo:hover {
    opacity: 0.8;
}

.nav-logo-img {
    height: 48px;
    width: auto;
}

/* Invert logo for dark mode */
[data-theme="dark"] .nav-logo-img {
    filter: invert(1);
}

.nav-links {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-left: auto;
    margin-right: var(--spacing-md);
}

.nav-link {
    font-family: var(--font-heading);
    font-size: 0.875rem;
    font-weight: 500;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

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

.nav-actions {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

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

.theme-toggle:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.icon-sun, .icon-moon {
    transition: opacity var(--transition-fast), transform var(--transition-fast);
}

[data-theme="light"] .icon-moon {
    display: none;
}

[data-theme="dark"] .icon-sun {
    display: none;
}

/* --------------------------------------------------------------------------
   Main Content Area
   -------------------------------------------------------------------------- */

.main-content {
    flex: 1;
}

/* --------------------------------------------------------------------------
   Homepage Styles
   -------------------------------------------------------------------------- */

.home-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-2xl) var(--spacing-lg);
}

.home-hero {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    padding: var(--spacing-2xl) 0;
}

.hero-logo {
    height: 80px;
    width: auto;
    margin-bottom: var(--spacing-md);
}

/* Invert hero logo for dark mode */
[data-theme="dark"] .hero-logo {
    filter: invert(1);
}

.hero-title {
    font-family: var(--font-heading);
    font-size: 3.5rem;
    font-weight: 700;
    letter-spacing: -0.03em;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
}

.hero-subtitle {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-lg);
}

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

.hero-description a {
    color: var(--color-primary);
    text-decoration: underline;
    text-underline-offset: 2px;
}

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

/* Force 4 columns for chapter grid */
.chapters-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--spacing-lg);
}

.chapter-card {
    display: flex;
    flex-direction: column;
    padding: var(--spacing-lg);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    transition: all var(--transition-normal);
    position: relative;
    overflow: hidden;
}

.chapter-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--chapter-color);
    opacity: 0;
    transition: opacity var(--transition-fast);
}

.chapter-card:hover {
    border-color: var(--chapter-color);
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
}

.chapter-card:hover::before {
    opacity: 1;
}

.card-header {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    margin-bottom: var(--spacing-md);
}

.card-number {
    font-family: var(--font-heading);
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--chapter-color);
    line-height: 1;
    opacity: 0.3;
}

.card-icon {
    width: 48px;
    height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: color-mix(in srgb, var(--chapter-color) 10%, transparent);
    border-radius: var(--radius-md);
    color: var(--chapter-color);
}

.card-title {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-sm);
}

.card-description {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    flex: 1;
    margin-bottom: var(--spacing-md);
}

.card-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--color-border-light);
}

.section-count {
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.card-arrow {
    color: var(--chapter-color);
    opacity: 0;
    transform: translateX(-8px);
    transition: all var(--transition-fast);
}

.chapter-card:hover .card-arrow {
    opacity: 1;
    transform: translateX(0);
}

/* --------------------------------------------------------------------------
   Chapter Layout (Sidebar + Content)
   -------------------------------------------------------------------------- */

.chapter-layout {
    display: flex;
    min-height: calc(100vh - var(--nav-height));
    position: relative;
}

.chapter-sidebar {
    width: var(--sidebar-width);
    min-width: 200px;
    max-width: 450px;
    flex-shrink: 0;
    background: var(--color-bg-secondary);
    border-right: 1px solid var(--color-border);
    position: sticky;
    top: var(--nav-height);
    height: calc(100vh - var(--nav-height));
    overflow-y: auto;
    transition: width 0.2s ease, min-width 0.2s ease;
}

.chapter-sidebar.collapsed {
    width: 0 !important;
    min-width: 0 !important;
    overflow: hidden;
    border-right: none;
}

.chapter-sidebar.resizing {
    transition: none;
}

/* Sidebar resize handle */
.sidebar-resize-handle {
    position: absolute;
    top: 0;
    right: 0;
    width: 4px;
    height: 100%;
    cursor: col-resize;
    z-index: 10;
    background: transparent;
    transition: background 0.15s ease;
}

.sidebar-resize-handle:hover,
.sidebar-resize-handle.active {
    background: var(--chapter-color, var(--color-primary));
}

/* Sidebar toggle button */
.sidebar-toggle {
    position: fixed;
    left: var(--sidebar-width);
    top: calc(var(--nav-height) + var(--spacing-md));
    z-index: 101;
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: left 0.2s ease, background 0.15s ease;
    color: var(--color-text-secondary);
}

.sidebar-toggle:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.sidebar-toggle.collapsed {
    left: var(--spacing-sm);
}

.sidebar-toggle svg {
    width: 14px;
    height: 14px;
    transition: transform 0.2s ease;
}

.sidebar-toggle.collapsed svg {
    transform: rotate(180deg);
}

/* --------------------------------------------------------------------------
   Right Sidebar (Download & Chat)
   -------------------------------------------------------------------------- */

.right-sidebar {
    position: fixed;
    right: 0;
    top: var(--nav-height);
    width: var(--right-sidebar-width);
    min-width: 240px;
    max-width: 400px;
    height: calc(100vh - var(--nav-height));
    background: var(--color-bg-secondary);
    border-left: 1px solid var(--color-border);
    display: flex;
    flex-direction: column;
    z-index: 99;
    transition: width 0.2s ease, min-width 0.2s ease, transform 0.2s ease;
}

.right-sidebar.collapsed {
    transform: translateX(100%);
}

.right-sidebar.resizing {
    transition: none;
}

/* Right sidebar resize handle */
.right-sidebar-resize-handle {
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    cursor: col-resize;
    z-index: 10;
    background: transparent;
    transition: background 0.15s ease;
}

.right-sidebar-resize-handle:hover,
.right-sidebar-resize-handle.active {
    background: var(--color-primary);
}

/* Right sidebar toggle button */
.right-sidebar-toggle {
    position: fixed;
    right: var(--right-sidebar-width);
    top: calc(var(--nav-height) + var(--spacing-md));
    z-index: 101;
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: right 0.2s ease, background 0.15s ease;
    color: var(--color-text-secondary);
}

.right-sidebar-toggle:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.right-sidebar-toggle.collapsed {
    right: var(--spacing-sm);
}

.right-sidebar-toggle svg {
    width: 14px;
    height: 14px;
    transition: transform 0.2s ease;
}

.right-sidebar-toggle.collapsed svg {
    transform: rotate(180deg);
}

/* Right sidebar sections */
.right-sidebar-section {
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--color-border);
}

.right-sidebar-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
    position: relative;
}

.right-sidebar-title {
    font-family: var(--font-heading);
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text);
}

/* Help button */
.help-button {
    width: 18px;
    height: 18px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    border: 1px solid var(--color-border);
    border-radius: 50%;
    cursor: pointer;
    color: var(--color-text-muted);
    font-size: 0.75rem;
    transition: all var(--transition-fast);
}

.help-button:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
    border-color: var(--color-text-muted);
}

.help-button.inline-help {
    width: 16px;
    height: 16px;
    font-size: 0.625rem;
    margin-left: auto;
}

/* Help tooltip */
.help-tooltip {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    margin-top: var(--spacing-xs);
    padding: var(--spacing-sm);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    font-size: 0.75rem;
    color: var(--color-text-secondary);
    box-shadow: var(--shadow-md);
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition-fast), visibility var(--transition-fast);
    z-index: 10;
}

.help-button:hover + .help-tooltip,
.help-tooltip:hover {
    opacity: 1;
    visibility: visible;
}

/* Inline help tooltip */
.help-button.inline-help[data-tooltip]:hover::after {
    content: attr(data-tooltip);
    position: absolute;
    bottom: 100%;
    right: 0;
    width: 200px;
    margin-bottom: var(--spacing-xs);
    padding: var(--spacing-sm);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    font-size: 0.75rem;
    color: var(--color-text-secondary);
    box-shadow: var(--shadow-md);
    z-index: 10;
}

/* Download options */
.download-options {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.download-option-group {
    display: flex;
    flex-direction: column;
    gap: 0;
}

.download-section-header {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-xs);
}

.download-sections {
    /* No max-height - expand to fit all content */
}

.download-btn-tokens {
    font-size: 0.75rem;
    opacity: 0.8;
    margin-left: var(--spacing-xs);
}

.download-btn-tokens:empty {
    display: none;
}

.download-option {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: 2px var(--spacing-sm);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.download-option:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.download-option input[type="radio"],
.download-option input[type="checkbox"] {
    accent-color: var(--chapter-color, var(--color-primary));
}

.download-option input[type="radio"]:disabled,
.download-option input[type="checkbox"]:disabled {
    opacity: 0.5;
}

.download-option:has(input:disabled) {
    opacity: 0.5;
    cursor: not-allowed;
}

.download-button {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--chapter-color, var(--color-primary));
    color: white;
    border: none;
    border-radius: var(--radius-md);
    font-family: var(--font-heading);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.download-button:hover {
    filter: brightness(1.1);
}

.download-button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Fix dark mode contrast - use dark text on light-colored buttons */
[data-theme="dark"] .download-button {
    color: #111111;
}

[data-theme="dark"] .chat-send-btn {
    color: #111111;
}

/* Download disabled overlay */
.download-section {
    position: relative;
}

.download-disabled-overlay {
    position: absolute;
    inset: 0;
    background: color-mix(in srgb, var(--color-bg-secondary) 85%, transparent);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 5;
    border-radius: var(--radius-md);
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition-fast), visibility var(--transition-fast);
}

.download-section.disabled .download-disabled-overlay {
    opacity: 1;
    visibility: visible;
}

.disabled-message {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md);
    text-align: center;
    font-size: 0.75rem;
    color: var(--color-text-muted);
}

/* Chat section */
.chat-section {
    flex: 1;
    display: flex;
    flex-direction: column;
    min-height: 0;
    overflow: hidden;
}

.chat-messages {
    flex: 1;
    overflow-y: auto;
    padding: var(--spacing-sm);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.chat-placeholder {
    color: var(--color-text-muted);
    font-size: 0.8125rem;
    font-style: italic;
    text-align: center;
    padding: var(--spacing-lg);
}

.chat-message {
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: 0.8125rem;
    line-height: 1.5;
    max-width: 90%;
    word-break: break-word;
    overflow-wrap: break-word;
}

.chat-message.user {
    background: var(--color-primary);
    color: white;
    align-self: flex-end;
    border-bottom-right-radius: var(--radius-sm);
}

[data-theme="dark"] .chat-message.user {
    color: #111111;
}

.chat-message.assistant {
    background: var(--color-bg-tertiary);
    color: var(--color-text);
    align-self: flex-start;
    border-bottom-left-radius: var(--radius-sm);
}

.chat-message.error {
    background: #fee2e2;
    color: #991b1b;
    border: 1px solid #fecaca;
}

[data-theme="dark"] .chat-message.error {
    background: #450a0a;
    color: #fca5a5;
    border-color: #7f1d1d;
}

.chat-model-select {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.75rem;
    color: var(--color-text-secondary);
}

.chat-model-select label {
    font-weight: 500;
}

.chat-model-select select {
    flex: 1;
    padding: 4px 8px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background: var(--color-surface);
    color: var(--color-text);
    font-family: var(--font-body);
    font-size: 0.75rem;
    cursor: pointer;
}

.chat-model-select select:focus {
    outline: none;
    border-color: var(--color-primary);
}

.chat-clear-btn {
    display: block;
    width: 100%;
    padding: var(--spacing-sm);
    margin-top: auto;
    background: transparent;
    border: none;
    border-top: 1px solid var(--color-border);
    color: var(--color-text-muted);
    font-size: 0.75rem;
    cursor: pointer;
    transition: all var(--transition-fast);
}

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

.chat-input-container {
    display: flex;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm);
    background: var(--color-bg-secondary);
}

.chat-input {
    flex: 1;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    background: var(--color-surface);
    color: var(--color-text);
    font-family: var(--font-body);
    font-size: 0.8125rem;
    resize: none;
    min-height: 36px;
    line-height: 1.4;
    overflow: hidden;
}

.chat-input:focus {
    outline: none;
    border-color: var(--color-primary);
}

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

.chat-send-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: var(--color-primary);
    color: white;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    flex-shrink: 0;
}

.chat-send-btn:hover {
    background: var(--color-primary-hover);
}

/* Adjust main content when right sidebar is open */
body:has(.right-sidebar:not(.collapsed)) .chapter-content {
    margin-right: var(--right-sidebar-width);
}

body:has(.right-sidebar:not(.collapsed)) .main-content:not(:has(.chapter-layout)) {
    margin-right: var(--right-sidebar-width);
}

.sidebar-header {
    padding: var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
}

.sidebar-title {
    font-family: var(--font-heading);
    font-size: 1rem;
    font-weight: 600;
    color: var(--chapter-color);
}

.sidebar-nav {
    padding: var(--spacing-md);
}

.section-list {
    list-style: none;
}

.section-list li {
    margin-bottom: 2px;
}

.section-link {
    display: flex;
    align-items: flex-start;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.section-link:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.section-link.active {
    background: color-mix(in srgb, var(--chapter-color) 10%, transparent);
    color: var(--chapter-color);
}

.section-number {
    font-family: var(--font-heading);
    font-weight: 600;
    font-size: 0.75rem;
    min-width: 2.5rem;
    opacity: 0.6;
}

.section-title {
    flex: 1;
    line-height: 1.4;
}

/* Section hierarchy (group sections with children) */
.section-group {
    margin-top: var(--spacing-sm);
}

.section-group:first-child {
    margin-top: 0;
}

.section-group > .section-link {
    font-weight: 600;
    color: var(--color-text);
}

.section-group > .section-link .section-number {
    opacity: 0.8;
}

/* Child sections with tree connector */
.section-child {
    position: relative;
    padding-left: var(--spacing-lg);
}

.section-tree-connector {
    position: absolute;
    left: calc(var(--spacing-md) + 0.75rem);
    top: 0;
    bottom: 50%;
    width: 12px;
    border-left: 1.5px solid var(--color-border);
    border-bottom: 1.5px solid var(--color-border);
    border-bottom-left-radius: 4px;
    pointer-events: none;
}

/* Extend the line for non-last children */
.section-child:not(:last-child) .section-tree-connector,
.section-child:has(+ .section-child) .section-tree-connector {
    bottom: -50%;
}

/* Vertical line through all children except the last */
.section-child:not(:last-child):not(:has(+ li:not(.section-child)))::before {
    content: '';
    position: absolute;
    left: calc(var(--spacing-md) + 0.75rem);
    top: 50%;
    bottom: -50%;
    border-left: 1.5px solid var(--color-border);
    pointer-events: none;
}

/* Handle the last child in a group - only show horizontal portion */
.section-child:has(+ li:not(.section-child)) .section-tree-connector,
.section-child:last-child .section-tree-connector {
    bottom: 50%;
}

.section-child > .section-link {
    padding-left: var(--spacing-sm);
}

.section-child > .section-link .section-number {
    font-size: 0.7rem;
    min-width: 2rem;
}

/* --------------------------------------------------------------------------
   Chapter Content Area
   -------------------------------------------------------------------------- */

.chapter-content {
    flex: 1;
    min-width: 0;
    padding: var(--spacing-xl);
}

.chapter-overview {
    max-width: var(--content-max-width);
    margin: 0 auto;
}

.overview-title {
    font-family: var(--font-heading);
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--spacing-md);
}

.overview-description {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-2xl);
}

.sections-preview h2 {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--spacing-lg);
}

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

.section-card {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-md) var(--spacing-lg);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.section-card:hover {
    border-color: var(--chapter-color);
    background: var(--color-surface-hover);
}

.section-card-number {
    font-family: var(--font-heading);
    font-weight: 600;
    font-size: 0.875rem;
    color: var(--chapter-color);
    min-width: 1.5rem;
}

.section-card-title {
    flex: 1;
    font-weight: 500;
    color: var(--color-text);
}

.section-card-arrow {
    color: var(--chapter-color);
    opacity: 0;
    transform: translateX(-4px);
    transition: all var(--transition-fast);
}

.section-card:hover .section-card-arrow {
    opacity: 1;
    transform: translateX(0);
}

/* --------------------------------------------------------------------------
   Markdown Content Styles
   -------------------------------------------------------------------------- */

.markdown-content {
    max-width: var(--content-max-width);
    margin: 0 auto;
}

.markdown-content h1 {
    font-family: var(--font-heading);
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-md);
    border-bottom: 2px solid var(--chapter-color, var(--color-border));
}

.markdown-content h2 {
    font-family: var(--font-heading);
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--color-text);
    margin-top: var(--spacing-2xl);
    margin-bottom: var(--spacing-md);
}

.markdown-content h3 {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text);
    margin-top: var(--spacing-xl);
    margin-bottom: var(--spacing-sm);
}

.markdown-content h4 {
    font-family: var(--font-heading);
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-text);
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
}

.markdown-content h5 {
    font-family: var(--font-heading);
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--color-text);
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
}

.markdown-content h6 {
    font-family: var(--font-heading);
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text);
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
}

.markdown-content p {
    margin-bottom: var(--spacing-md);
    color: var(--color-text);
}

.markdown-content a {
    color: var(--color-primary);
    text-decoration: underline;
    text-underline-offset: 2px;
}

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

.markdown-content ul, .markdown-content ol {
    margin-bottom: var(--spacing-md);
    padding-left: var(--spacing-xl);
}

.markdown-content li {
    margin-bottom: var(--spacing-xs);
}

.markdown-content blockquote {
    margin: var(--spacing-sm) 0;
    padding: var(--spacing-sm) var(--spacing-md);
    border-left: 4px solid var(--chapter-color, var(--color-primary));
    background: var(--color-bg-secondary);
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
}

.markdown-content blockquote p:last-child {
    margin-bottom: 0;
}

.markdown-content code {
    font-family: var(--font-mono);
    font-size: 0.875em;
    padding: 0.2em 0.4em;
    background: var(--color-bg-tertiary);
    border-radius: var(--radius-sm);
}

.markdown-content pre {
    margin: var(--spacing-md) 0;
    padding: var(--spacing-md);
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow-x: auto;
}

.markdown-content pre code {
    padding: 0;
    background: transparent;
    font-size: 0.875rem;
    line-height: 1.6;
}

/* Pygments syntax highlighting - Light theme (SAS-inspired) */
.codehilite {
    background: var(--color-bg-secondary);
    margin: var(--spacing-md) 0;
    padding: var(--spacing-md);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    overflow-x: auto;
}

.codehilite pre {
    margin: 0;
    padding: 0;
    background: transparent;
    border: none;
}

/* Pygments syntax highlighting token colors are in pygments.css */

.markdown-content table {
    width: 100%;
    margin: var(--spacing-lg) 0;
    border-collapse: collapse;
    font-size: 0.875rem;
}

.markdown-content th, .markdown-content td {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--color-border);
    text-align: left;
}

.markdown-content th {
    font-family: var(--font-heading);
    font-weight: 600;
    background: var(--color-bg-secondary);
}

.markdown-content img {
    border-radius: var(--radius-md);
    margin: var(--spacing-lg) 0;
}

.markdown-content hr {
    margin: var(--spacing-2xl) 0;
    border: none;
    border-top: 1px solid var(--color-border);
}

/* KaTeX display math wrapper - for protected LaTeX blocks */
.markdown-content .katex-display-wrapper {
    display: block;
    margin: var(--spacing-lg) 0;
    text-align: center;
    overflow-x: auto;
    overflow-y: hidden;
    padding: var(--spacing-sm) 0;
}

/* KaTeX display math - ensure multi-line rendering */
.markdown-content .katex-display {
    display: block;
    margin: var(--spacing-md) 0;
    text-align: center;
    overflow-x: auto;
    overflow-y: hidden;
}

.markdown-content .katex-display > .katex {
    display: inline-block;
    white-space: normal;
    text-align: left;
}

.markdown-content .katex-display .base {
    display: inline-block;
}

/* Ensure display math has proper line breaking */
.markdown-content .katex .mord,
.markdown-content .katex .mrel,
.markdown-content .katex .mbin,
.markdown-content .katex .mopen,
.markdown-content .katex .mclose {
    display: inline;
}

/* --------------------------------------------------------------------------
   Content Navigation (Prev/Next)
   -------------------------------------------------------------------------- */

.content-nav {
    display: flex;
    justify-content: space-between;
    gap: var(--spacing-lg);
    margin-top: var(--spacing-2xl);
    padding-top: var(--spacing-xl);
    border-top: 1px solid var(--color-border);
}

.nav-prev, .nav-next {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.nav-prev:hover, .nav-next:hover {
    color: var(--chapter-color);
    background: color-mix(in srgb, var(--chapter-color) 10%, transparent);
}

.nav-next {
    margin-left: auto;
}

/* --------------------------------------------------------------------------
   FAQ Page
   -------------------------------------------------------------------------- */

.faq-container {
    max-width: var(--content-max-width);
    margin: 0 auto;
    padding: var(--spacing-2xl) var(--spacing-lg);
}

.faq-container h1 {
    font-family: var(--font-heading);
    font-size: 2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--spacing-lg);
}

.faq-placeholder {
    color: var(--color-text-secondary);
    font-size: 1.125rem;
}

/* --------------------------------------------------------------------------
   Footer
   -------------------------------------------------------------------------- */

.site-footer {
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-lg);
    margin-top: auto;
}

.footer-container {
    max-width: 1400px;
    margin: 0 auto;
    text-align: center;
}

.site-footer p {
    font-size: 0.875rem;
    color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   Subsection Navigation
   -------------------------------------------------------------------------- */

.sidebar-subsections {
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-md);
}

.subsection-header {
    padding: var(--spacing-sm) var(--spacing-md);
    margin-bottom: var(--spacing-xs);
}

.subsection-header-title {
    font-family: var(--font-heading);
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-muted);
}

.subsection-list {
    list-style: none;
}

.subsection-list li {
    margin-bottom: var(--spacing-xs);
}

.subsection-link {
    display: block;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
    border-left: 2px solid transparent;
}

.subsection-link:hover {
    background: var(--color-surface-hover);
    color: var(--color-text);
}

.subsection-link.active {
    background: color-mix(in srgb, var(--chapter-color) 10%, transparent);
    color: var(--chapter-color);
    border-left-color: var(--chapter-color);
}

.subsection-title {
    display: block;
    line-height: 1.4;
}

/* --------------------------------------------------------------------------
   Table of Contents
   -------------------------------------------------------------------------- */

.sidebar-toc {
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-md);
}

.toc-header {
    padding: var(--spacing-sm) var(--spacing-md);
    margin-bottom: var(--spacing-xs);
}

.toc-header-title {
    font-family: var(--font-heading);
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-muted);
}

.toc-list {
    list-style: none;
}

.toc-item {
    margin-bottom: 0;
}

/* Hide h1 headers from TOC - only show h2 and below */
.toc-item.toc-level-1 {
    display: none;
}

/* Add slightly more spacing above h2 headers in TOC */
.toc-item.toc-level-2:not(:first-child) {
    margin-top: var(--spacing-xs);
}

.toc-link {
    display: block;
    padding: var(--spacing-xs) var(--spacing-md);
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
    border-radius: var(--radius-sm);
    line-height: 1.3;
}

.toc-link:hover {
    color: var(--color-text);
    background: var(--color-surface-hover);
}

/* TOC indentation based on header level */
.toc-level-2 .toc-link {
    padding-left: var(--spacing-md);
}

.toc-level-3 .toc-link {
    padding-left: calc(var(--spacing-md) + var(--spacing-sm));
    font-size: 0.75rem;
}

.toc-level-4 .toc-link {
    padding-left: calc(var(--spacing-md) + var(--spacing-md));
    font-size: 0.75rem;
    color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   Loading Indicator
   -------------------------------------------------------------------------- */

.loading-indicator {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-2xl);
    color: var(--color-text-secondary);
}

.loading-spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--color-border);
    border-top-color: var(--chapter-color, var(--color-primary));
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    margin-bottom: var(--spacing-md);
}

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

.error-message {
    padding: var(--spacing-xl);
    text-align: center;
    color: var(--color-text-secondary);
}

/* --------------------------------------------------------------------------
   Details/Summary Elements
   -------------------------------------------------------------------------- */

.markdown-content details {
    margin: var(--spacing-md) 0;
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
}

.markdown-content details summary {
    cursor: pointer;
    font-weight: 500;
    color: var(--color-text);
    padding: var(--spacing-xs) 0;
    list-style: none;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.markdown-content details summary::-webkit-details-marker {
    display: none;
}

.markdown-content details summary::before {
    content: '▶';
    font-size: 0.75em;
    transition: transform var(--transition-fast);
}

.markdown-content details[open] summary::before {
    transform: rotate(90deg);
}

.markdown-content details[open] summary {
    margin-bottom: var(--spacing-sm);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid var(--color-border);
}

/* Code blocks inside details should blend in without extra border/box */
.markdown-content details .codehilite {
    margin: var(--spacing-sm) 0;
    padding: var(--spacing-sm);
    border: none;
    background: transparent;
}

/* --------------------------------------------------------------------------
   Exercise Info Blocks
   -------------------------------------------------------------------------- */

.exercise-info {
    margin: var(--spacing-md) 0;
    padding: var(--spacing-sm) var(--spacing-md);
    background: color-mix(in srgb, var(--chapter-color, var(--color-primary)) 8%, var(--color-bg-secondary));
    border-left: 4px solid var(--chapter-color, var(--color-primary));
    border-radius: var(--radius-md);
}

.exercise-info-row {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-xs);
}

.exercise-info-label {
    font-weight: 600;
    font-size: 0.875rem;
    color: var(--color-text);
    min-width: 90px;
}

.exercise-info-value {
    font-size: 1rem;
    letter-spacing: 0.1em;
}

.exercise-info-description {
    margin-top: var(--spacing-sm);
    padding-top: var(--spacing-sm);
    border-top: 1px solid var(--color-border);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    font-style: italic;
}

/* --------------------------------------------------------------------------
   Responsive Design
   -------------------------------------------------------------------------- */

@media (max-width: 1100px) {
    .chapters-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    :root {
        --nav-height: 56px;
    }

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

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

    .chapter-sidebar {
        width: 100% !important;
        min-width: 100% !important;
        max-width: 100% !important;
        position: relative;
        top: 0;
        height: auto;
        max-height: 50vh;
        overflow-y: auto;
    }

    .chapter-sidebar.collapsed {
        width: 100% !important;
        min-width: 100% !important;
        overflow-y: auto;
        border-right: none;
    }

    .sidebar-toggle,
    .sidebar-resize-handle {
        display: none;
    }

    .sidebar-toc {
        display: none;
    }

    .right-sidebar,
    .right-sidebar-toggle,
    .right-sidebar-resize-handle {
        display: none;
    }

    body:has(.right-sidebar:not(.collapsed)) .chapter-content,
    body:has(.right-sidebar:not(.collapsed)) .main-content:not(:has(.chapter-layout)) {
        margin-right: 0;
    }

    .chapter-content {
        padding: var(--spacing-lg);
    }

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

    .nav-next {
        margin-left: 0;
    }

    .hero-logo {
        height: 60px;
    }
}

@media (max-width: 560px) {
    .home-container {
        padding: var(--spacing-lg) var(--spacing-md);
    }

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

    .nav-links {
        display: none;
    }
}