/* ===================================================
   System Design Primer — Interactive Course Styles
   Modern, responsive, dark/light theme, shadcn-inspired
   =================================================== */

/* --- CSS Custom Properties (Theme) --- */
:root {
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;

    /* Sizing */
    --sidebar-width: 300px;
    --topbar-height: 56px;
    --content-max-width: 820px;
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 350ms ease;
}

/* Dark Theme (default) */
[data-theme="dark"] {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #1c2129;
    --bg-elevated: #21262d;
    --bg-hover: #292e36;
    --bg-active: #1f6feb22;

    --border-primary: #30363d;
    --border-secondary: #21262d;
    --border-accent: #1f6feb;

    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-tertiary: #6e7681;
    --text-link: #58a6ff;
    --text-on-accent: #ffffff;

    --accent: #1f6feb;
    --accent-hover: #388bfd;
    --accent-subtle: #1f6feb22;
    --success: #3fb950;
    --success-subtle: #3fb95022;
    --warning: #d29922;
    --warning-subtle: #d2992222;
    --danger: #f85149;

    --code-bg: #161b22;
    --code-border: #30363d;

    --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
    --shadow-lg: 0 8px 24px rgba(0,0,0,0.5);

    --scrollbar-thumb: #30363d;
    --scrollbar-track: transparent;
}

/* Light Theme */
[data-theme="light"] {
    --bg-primary: #ffffff;
    --bg-secondary: #f6f8fa;
    --bg-tertiary: #f0f2f5;
    --bg-elevated: #ffffff;
    --bg-hover: #eaeef2;
    --bg-active: #0969da15;

    --border-primary: #d0d7de;
    --border-secondary: #e8ebef;
    --border-accent: #0969da;

    --text-primary: #1f2328;
    --text-secondary: #656d76;
    --text-tertiary: #8c959f;
    --text-link: #0969da;
    --text-on-accent: #ffffff;

    --accent: #0969da;
    --accent-hover: #0550ae;
    --accent-subtle: #0969da15;
    --success: #1a7f37;
    --success-subtle: #1a7f3715;
    --warning: #9a6700;
    --warning-subtle: #9a670015;
    --danger: #cf222e;

    --code-bg: #f6f8fa;
    --code-border: #d0d7de;

    --shadow-sm: 0 1px 2px rgba(0,0,0,0.06);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
    --shadow-lg: 0 8px 24px rgba(0,0,0,0.12);

    --scrollbar-thumb: #c1c8cf;
    --scrollbar-track: transparent;
}

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

html {
    font-size: 16px;
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    overflow-x: hidden;
    transition: background var(--transition-normal), color var(--transition-normal);
}

/* Custom Scrollbar */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}
::-webkit-scrollbar-track {
    background: var(--scrollbar-track);
}
::-webkit-scrollbar-thumb {
    background: var(--scrollbar-thumb);
    border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
    background: var(--text-tertiary);
}

/* Selection */
::selection {
    background: var(--accent);
    color: var(--text-on-accent);
}

/* ===================================
   SIDEBAR (docs page)
   =================================== */
.sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: var(--sidebar-width);
    height: 100vh;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border-primary);
    display: flex;
    flex-direction: column;
    z-index: 100;
    transition: transform var(--transition-normal), background var(--transition-normal);
    overflow: hidden;
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 16px 12px;
    border-bottom: 1px solid var(--border-secondary);
    flex-shrink: 0;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    color: inherit;
    transition: opacity var(--transition-fast);
}

.logo:hover {
    opacity: 0.8;
}

.logo-icon {
    font-size: 28px;
    line-height: 1;
}

.logo-text {
    font-size: 15px;
    font-weight: 700;
    line-height: 1.2;
    color: var(--text-primary);
}

.logo-text small {
    font-weight: 500;
    color: var(--text-secondary);
    font-size: 12px;
}

.sidebar-close {
    display: none;
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 4px;
    border-radius: var(--radius-sm);
    transition: color var(--transition-fast), background var(--transition-fast);
}
.sidebar-close:hover {
    color: var(--text-primary);
    background: var(--bg-hover);
}

/* Sidebar Search */
.sidebar-search {
    padding: 12px 16px 8px;
    flex-shrink: 0;
    position: relative;
}

.search-input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

.search-icon {
    position: absolute;
    left: 10px;
    color: var(--text-tertiary);
    pointer-events: none;
}

.search-input-wrapper input {
    width: 100%;
    padding: 8px 12px 8px 34px;
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-sm);
    background: var(--bg-primary);
    color: var(--text-primary);
    font-family: var(--font-sans);
    font-size: 13px;
    outline: none;
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

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

.search-input-wrapper input:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-subtle);
}

/* Progress */
.sidebar-progress {
    padding: 8px 16px 12px;
    flex-shrink: 0;
}

.progress-bar {
    height: 4px;
    background: var(--bg-elevated);
    border-radius: 2px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    width: 0%;
    background: linear-gradient(90deg, var(--accent), var(--success));
    border-radius: 2px;
    transition: width var(--transition-slow);
}

.progress-text {
    font-size: 11px;
    color: var(--text-tertiary);
    margin-top: 4px;
    display: block;
}

/* Sidebar Nav */
.sidebar-nav {
    flex: 1;
    overflow-y: auto;
    padding: 4px 8px;
}

.nav-group {
    margin-bottom: 2px;
}

.nav-group-header {
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 8px 8px;
    cursor: pointer;
    border-radius: var(--radius-sm);
    user-select: none;
    transition: background var(--transition-fast);
}

.nav-group-header:hover {
    background: var(--bg-hover);
}

.nav-group-icon {
    display: flex;
    align-items: center;
    color: var(--text-tertiary);
    transition: transform var(--transition-fast);
}

.nav-group-items.collapsed + .nav-group-header .nav-group-icon,
.nav-group-header.collapsed .nav-group-icon {
    transform: rotate(-90deg);
}

.nav-group-label {
    font-size: 11px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    flex: 1;
}

.nav-group-badge {
    font-size: 10px;
    font-weight: 600;
    color: var(--text-tertiary);
    background: var(--bg-elevated);
    padding: 1px 6px;
    border-radius: 10px;
}

.nav-group-items {
    overflow: hidden;
    max-height: 1000px;
    transition: max-height var(--transition-slow);
}

.nav-group-items.collapsed {
    max-height: 0;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 7px 8px 7px 18px;
    border-radius: var(--radius-sm);
    text-decoration: none;
    color: var(--text-secondary);
    font-size: 13px;
    font-weight: 400;
    transition: all var(--transition-fast);
    position: relative;
}

.nav-item:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.nav-item.active {
    background: var(--accent-subtle);
    color: var(--accent);
    font-weight: 500;
}

.nav-item.active::before {
    content: '';
    position: absolute;
    left: 0;
    top: 4px;
    bottom: 4px;
    width: 3px;
    background: var(--accent);
    border-radius: 2px;
}

.nav-item-status {
    width: 16px;
    height: 16px;
    border-radius: 50%;
    border: 2px solid var(--border-primary);
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition-fast);
}

.nav-item-status.completed {
    background: var(--success);
    border-color: var(--success);
}

.nav-item-status.completed::after {
    content: '';
    width: 6px;
    height: 3px;
    border-left: 2px solid white;
    border-bottom: 2px solid white;
    transform: rotate(-45deg) translateY(-1px);
}

.nav-item-number {
    font-size: 10px;
    font-weight: 600;
    color: var(--text-tertiary);
    font-family: var(--font-mono);
    min-width: 18px;
}

.nav-item-label {
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.nav-item.hidden {
    display: none;
}

/* Theme toggle in topbar */
.theme-toggle-topbar {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
    flex-shrink: 0;
}

.theme-toggle-topbar:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
    border-color: var(--accent);
}

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

/* --- Sidebar Overlay (mobile) --- */
.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.5);
    z-index: 99;
    backdrop-filter: blur(2px);
}
.sidebar-overlay.active {
    display: block;
}

/* ===================================
   MAIN CONTENT (docs page)
   =================================== */
.main-content {
    margin-left: var(--sidebar-width);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    transition: margin var(--transition-normal);
}

/* Top Bar */
.topbar {
    position: sticky;
    top: 0;
    z-index: 50;
    display: flex;
    align-items: center;
    gap: 12px;
    height: var(--topbar-height);
    padding: 0 24px;
    border-bottom: 1px solid var(--border-secondary);
    backdrop-filter: blur(12px);
    background: color-mix(in srgb, var(--bg-primary) 85%, transparent);
    transition: background var(--transition-normal);
}

.menu-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 4px;
    border-radius: var(--radius-sm);
    transition: color var(--transition-fast);
}
.menu-toggle:hover {
    color: var(--text-primary);
}

.breadcrumb {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 14px;
    flex: 1;
    min-width: 0;
}

.breadcrumb-part {
    color: var(--text-tertiary);
    font-weight: 500;
    white-space: nowrap;
}

.breadcrumb svg {
    color: var(--text-tertiary);
    flex-shrink: 0;
}

.breadcrumb-chapter {
    color: var(--text-primary);
    font-weight: 600;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.topbar-actions {
    flex-shrink: 0;
    display: flex;
    align-items: center;
    gap: 8px;
}

.btn-mark-complete {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 6px 14px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 13px;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-mark-complete:hover {
    background: var(--success-subtle);
    border-color: var(--success);
    color: var(--success);
}

.btn-mark-complete.completed {
    background: var(--success);
    border-color: var(--success);
    color: white;
}

/* Notes Toggle Button */
.btn-notes-toggle {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 6px 14px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 13px;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-notes-toggle:hover {
    background: var(--accent-subtle);
    border-color: var(--accent);
    color: var(--accent);
}

.btn-notes-toggle.has-notes {
    color: var(--accent);
    border-color: var(--accent);
}

/* Content Area */
.content-area {
    flex: 1;
    overflow-y: auto;
    padding: 32px 24px 64px;
}

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

/* ===================================
   CHAPTER CONTENT STYLES
   =================================== */
.chapter-content {
    animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(8px); }
    to { opacity: 1; transform: translateY(0); }
}

.chapter-content .chapter-badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 12px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--accent);
    background: var(--accent-subtle);
    margin-bottom: 12px;
}

.chapter-content h1 {
    font-size: 2rem;
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: 8px;
    color: var(--text-primary);
    letter-spacing: -0.02em;
}

.chapter-content .chapter-subtitle {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 32px;
    line-height: 1.6;
}

.chapter-content h2 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-top: 48px;
    margin-bottom: 16px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border-secondary);
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

.chapter-content h3 {
    font-size: 1.2rem;
    font-weight: 600;
    margin-top: 32px;
    margin-bottom: 12px;
    color: var(--text-primary);
}

.chapter-content h4 {
    font-size: 1.05rem;
    font-weight: 600;
    margin-top: 24px;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.chapter-content p {
    margin-bottom: 16px;
    color: var(--text-primary);
    line-height: 1.75;
}

.chapter-content ul, .chapter-content ol {
    margin-bottom: 16px;
    padding-left: 24px;
}

.chapter-content li {
    margin-bottom: 6px;
    color: var(--text-primary);
    line-height: 1.65;
}

.chapter-content li ul, .chapter-content li ol {
    margin-top: 6px;
    margin-bottom: 6px;
}

.chapter-content strong {
    font-weight: 600;
    color: var(--text-primary);
}

.chapter-content a {
    color: var(--text-link);
    text-decoration: none;
    font-weight: 500;
    transition: opacity var(--transition-fast);
}
.chapter-content a:hover {
    opacity: 0.8;
    text-decoration: underline;
}

.chapter-content code {
    font-family: var(--font-mono);
    font-size: 0.875em;
    background: var(--code-bg);
    border: 1px solid var(--code-border);
    padding: 2px 6px;
    border-radius: 4px;
    color: var(--text-link);
}

.chapter-content pre {
    background: var(--code-bg);
    border: 1px solid var(--code-border);
    border-radius: var(--radius-md);
    padding: 16px 20px;
    overflow-x: auto;
    margin-bottom: 20px;
    line-height: 1.5;
}

.chapter-content pre code {
    background: none;
    border: none;
    padding: 0;
    font-size: 13px;
    color: var(--text-primary);
}

/* Images in chapters */
.chapter-content .img-container {
    margin: 24px 0;
    text-align: center;
}

.chapter-content .img-container img {
    max-width: 100%;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-primary);
    cursor: zoom-in;
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.chapter-content .img-container img:hover {
    box-shadow: var(--shadow-md);
}

.chapter-content .img-caption {
    font-size: 13px;
    color: var(--text-tertiary);
    margin-top: 8px;
    font-style: italic;
}

/* ===================================
   SHADCN-INSPIRED COMPONENTS (global)
   =================================== */

/* --- Cards --- */
.shadcn-card,
.concept-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: calc(var(--radius-md) + 2px);
    padding: 24px;
    margin-bottom: 20px;
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.shadcn-card:hover,
.concept-card:hover {
    border-color: color-mix(in srgb, var(--border-primary) 50%, var(--accent));
    box-shadow: var(--shadow-sm);
    transform: translateY(-1px);
}

.shadcn-card-header,
.concept-card .concept-card-icon + h4 {
    margin-bottom: 12px;
}

.shadcn-card-title {
    font-size: 18px;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0 0 4px;
}

.shadcn-card-description {
    font-size: 14px;
    color: var(--text-secondary);
    margin: 0;
    line-height: 1.5;
}

.shadcn-card-content {
    font-size: 14px;
    line-height: 1.7;
    color: var(--text-primary);
}

.shadcn-card-content p {
    margin-bottom: 12px;
}

/* Concept cards grid (shadcn-aligned) */
.concept-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 16px;
    margin: 24px 0;
}

.concept-card-icon {
    font-size: 24px;
    margin-bottom: 10px;
}

.concept-card h4 {
    margin: 0 0 6px;
    font-size: 15px;
    font-weight: 600;
    color: var(--text-primary);
}

.concept-card p {
    margin: 0;
    font-size: 13px;
    color: var(--text-secondary);
    line-height: 1.5;
}

/* --- Badges --- */
.shadcn-badge {
    display: inline-flex;
    align-items: center;
    padding: 2px 10px;
    border-radius: 9999px;
    font-size: 12px;
    font-weight: 500;
    line-height: 1.6;
    transition: background var(--transition-fast);
}

.shadcn-badge-default {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid var(--border-primary);
}

.shadcn-badge-blue {
    background: var(--accent-subtle);
    color: var(--accent);
    border: 1px solid transparent;
}

.shadcn-badge-green {
    background: var(--success-subtle);
    color: var(--success);
    border: 1px solid transparent;
}

.shadcn-badge-amber {
    background: var(--warning-subtle);
    color: var(--warning);
    border: 1px solid transparent;
}

/* --- Separator --- */
.shadcn-separator {
    height: 1px;
    background: var(--border-primary);
    margin: 24px 0;
    border: none;
}

/* --- Alerts (also applies to .callout for backward compat) --- */
.shadcn-alert,
.callout {
    position: relative;
    padding: 16px 20px;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    margin-bottom: 20px;
    font-size: 14px;
}

.shadcn-alert-info,
.callout-info {
    border-color: var(--accent);
    background: var(--accent-subtle);
    color: var(--text-primary);
}

.callout-tip {
    border-color: var(--success);
    background: var(--success-subtle);
    color: var(--text-primary);
}

.callout-warning {
    border-color: var(--warning);
    background: var(--warning-subtle);
    color: var(--text-primary);
}

.shadcn-alert-title,
.callout-title {
    font-size: 14px;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0 0 4px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.shadcn-alert-description {
    font-size: 13px;
    color: var(--text-secondary);
    margin: 0;
    line-height: 1.6;
    padding-left: 26px;
}

/* --- Tabs --- */
.shadcn-tabs {
    margin: 24px 0;
}

.shadcn-tabs-list {
    display: inline-flex;
    background: var(--bg-tertiary);
    border-radius: var(--radius-md);
    padding: 4px;
    gap: 0;
    margin-bottom: 16px;
}

.shadcn-tab-trigger {
    padding: 8px 16px;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 13px;
    font-weight: 500;
    cursor: pointer;
    border-radius: calc(var(--radius-md) - 2px);
    transition: all var(--transition-fast);
}

.shadcn-tab-trigger:hover {
    color: var(--text-primary);
}

.shadcn-tab-trigger.active {
    background: var(--bg-elevated);
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
}

.shadcn-tab-content {
    display: none;
}

.shadcn-tab-content.active {
    display: block;
    animation: fadeIn 0.2s ease;
}

/* --- Comparison Grid --- */
.shadcn-comparison-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin: 16px 0;
}

/* --- Tables --- */
.chapter-content table {
    width: 100%;
    border-collapse: collapse;
    margin-bottom: 20px;
    font-size: 14px;
}

.chapter-content .table-wrapper {
    overflow-x: auto;
    margin-bottom: 20px;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-primary);
}

.chapter-content table th {
    background: var(--bg-tertiary);
    font-weight: 600;
    text-align: left;
    padding: 10px 14px;
    border-bottom: 1px solid var(--border-primary);
    color: var(--text-primary);
    white-space: nowrap;
}

.chapter-content table td {
    padding: 10px 14px;
    border-bottom: 1px solid var(--border-secondary);
    color: var(--text-primary);
}

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

.chapter-content table tr:hover td {
    background: var(--bg-hover);
}

/* --- Accordions --- */
.accordion {
    margin-bottom: 12px;
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    overflow: hidden;
}

.accordion-header {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 14px 16px;
    background: var(--bg-secondary);
    cursor: pointer;
    font-weight: 600;
    font-size: 15px;
    color: var(--text-primary);
    transition: background var(--transition-fast);
    user-select: none;
}

.accordion-header:hover {
    background: var(--bg-hover);
}

.accordion-icon {
    transition: transform var(--transition-fast);
    color: var(--text-tertiary);
}

.accordion-header.open .accordion-icon {
    transform: rotate(90deg);
}

.accordion-body {
    max-height: 0;
    overflow: hidden;
    transition: max-height var(--transition-slow);
}

.accordion-body.open {
    max-height: 2000px;
}

.accordion-body-inner {
    padding: 16px;
    border-top: 1px solid var(--border-secondary);
}

/* Resource links */
.resource-list {
    list-style: none;
    padding: 0;
    margin: 16px 0;
}

.resource-list li {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 0;
    border-bottom: 1px solid var(--border-secondary);
}

.resource-list li:last-child {
    border-bottom: none;
}

.resource-list a {
    color: var(--text-link);
    text-decoration: none;
    font-weight: 500;
    font-size: 14px;
}

.resource-list a:hover {
    text-decoration: underline;
}

.resource-icon {
    color: var(--text-tertiary);
    flex-shrink: 0;
}

/* ===================================
   CHAPTER NAVIGATION (prev/next)
   =================================== */
.chapter-nav {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    margin-top: 48px;
    padding-top: 24px;
    border-top: 1px solid var(--border-secondary);
}

.chapter-nav-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px 20px;
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-family: var(--font-sans);
    cursor: pointer;
    transition: all var(--transition-fast);
    max-width: 48%;
}

.chapter-nav-btn:hover:not(:disabled) {
    border-color: var(--accent);
    background: var(--accent-subtle);
}

.chapter-nav-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.chapter-nav-btn svg {
    color: var(--text-tertiary);
    flex-shrink: 0;
}

.chapter-nav-text {
    display: flex;
    flex-direction: column;
    min-width: 0;
}

.chapter-nav-text small {
    font-size: 11px;
    color: var(--text-tertiary);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.chapter-nav-text span {
    font-size: 14px;
    font-weight: 600;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.chapter-nav-btn.next {
    margin-left: auto;
    text-align: right;
}

.chapter-nav-btn.next .chapter-nav-text {
    align-items: flex-end;
}

/* ===================================
   BACK TO TOP
   =================================== */
.back-to-top {
    position: fixed;
    bottom: 24px;
    right: 24px;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: var(--accent);
    color: white;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    transform: translateY(12px);
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-md);
    z-index: 40;
}

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

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

/* ===================================
   LIGHTBOX
   =================================== */
.lightbox {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.85);
    z-index: 200;
    align-items: center;
    justify-content: center;
    cursor: zoom-out;
    backdrop-filter: blur(4px);
    padding: 24px;
}

.lightbox.active {
    display: flex;
}

.lightbox-close {
    position: absolute;
    top: 16px;
    right: 20px;
    background: none;
    border: none;
    color: white;
    font-size: 32px;
    cursor: pointer;
    opacity: 0.7;
    transition: opacity var(--transition-fast);
}

.lightbox-close:hover {
    opacity: 1;
}

.lightbox-img {
    max-width: 90vw;
    max-height: 90vh;
    border-radius: var(--radius-md);
    object-fit: contain;
}

/* ===================================
   LOADING / COMING SOON
   =================================== */
.loading-spinner {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 80px 0;
    color: var(--text-tertiary);
}

.spinner {
    width: 32px;
    height: 32px;
    border: 3px solid var(--border-primary);
    border-top-color: var(--accent);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    margin-bottom: 12px;
}

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

.coming-soon {
    text-align: center;
    padding: 80px 20px;
}

.coming-soon-icon {
    font-size: 48px;
    margin-bottom: 16px;
}

.coming-soon h2 {
    border: none;
    margin-top: 0;
    font-size: 1.5rem;
}

.coming-soon p {
    color: var(--text-secondary);
    font-size: 15px;
}

/* ===================================
   NOTES PANEL (slide-in from right)
   =================================== */
.notes-panel {
    position: fixed;
    top: 0;
    right: 0;
    width: 380px;
    max-width: 90vw;
    height: 100vh;
    background: var(--bg-secondary);
    border-left: 1px solid var(--border-primary);
    z-index: 150;
    display: flex;
    flex-direction: column;
    transform: translateX(100%);
    transition: transform var(--transition-normal);
    box-shadow: var(--shadow-lg);
}

.notes-panel.open {
    transform: translateX(0);
}

.notes-panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 20px;
    border-bottom: 1px solid var(--border-primary);
    flex-shrink: 0;
}

.notes-panel-header h3 {
    font-size: 16px;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0;
}

.notes-panel-close {
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 4px;
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.notes-panel-close:hover {
    color: var(--text-primary);
    background: var(--bg-hover);
}

.notes-panel-chapter {
    padding: 10px 20px;
    font-size: 12px;
    color: var(--text-tertiary);
    border-bottom: 1px solid var(--border-secondary);
    flex-shrink: 0;
    font-weight: 500;
}

.notes-textarea {
    flex: 1;
    padding: 16px 20px;
    background: var(--bg-primary);
    color: var(--text-primary);
    border: none;
    resize: none;
    font-family: var(--font-sans);
    font-size: 14px;
    line-height: 1.7;
    outline: none;
}

.notes-textarea::placeholder {
    color: var(--text-tertiary);
}

.notes-panel-footer {
    padding: 10px 20px;
    border-top: 1px solid var(--border-secondary);
    flex-shrink: 0;
}

.notes-saved-indicator {
    font-size: 12px;
    color: var(--success);
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 4px;
}

.notes-saved-indicator::before {
    content: '\2713';
    font-weight: bold;
}

.notes-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.3);
    z-index: 140;
    backdrop-filter: blur(2px);
}

.notes-overlay.active {
    display: block;
}

/* ===================================
   HOMEPAGE — Standalone Page Styles
   =================================== */
.homepage-body {
    overflow-x: hidden;
}

/* Homepage nav bar */
.homepage-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 32px;
    backdrop-filter: blur(12px);
    background: color-mix(in srgb, var(--bg-primary) 70%, transparent);
    border-bottom: 1px solid color-mix(in srgb, var(--border-primary) 50%, transparent);
}

.homepage-nav-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    color: var(--text-primary);
    font-size: 15px;
    font-weight: 700;
    transition: opacity var(--transition-fast);
}

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

.homepage-nav-logo .logo-icon {
    font-size: 24px;
}

.homepage-nav-actions {
    display: flex;
    align-items: center;
    gap: 12px;
}

.homepage-nav-link {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

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

.homepage-theme-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-primary);
    background: color-mix(in srgb, var(--bg-secondary) 80%, transparent);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.homepage-theme-toggle:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
    border-color: var(--accent);
}

/* Hero section */
.homepage-hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
}

/* Animated grid background */
.homepage-bg {
    position: absolute;
    inset: 0;
    overflow: hidden;
}

.homepage-grid {
    position: absolute;
    inset: -50%;
    background-image:
        linear-gradient(var(--border-secondary) 1px, transparent 1px),
        linear-gradient(90deg, var(--border-secondary) 1px, transparent 1px);
    background-size: 60px 60px;
    animation: gridMove 20s linear infinite;
    opacity: 0.5;
}

@keyframes gridMove {
    0% { transform: translate(0, 0); }
    100% { transform: translate(60px, 60px); }
}

.homepage-glow {
    position: absolute;
    border-radius: 50%;
    filter: blur(80px);
    opacity: 0.15;
    animation: glowPulse 6s ease-in-out infinite alternate;
}

.homepage-glow-1 {
    width: 500px;
    height: 500px;
    background: var(--accent);
    top: -10%;
    left: -5%;
    animation-delay: 0s;
}

.homepage-glow-2 {
    width: 400px;
    height: 400px;
    background: #a855f7;
    bottom: -10%;
    right: -5%;
    animation-delay: 2s;
}

.homepage-glow-3 {
    width: 300px;
    height: 300px;
    background: var(--success);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    animation-delay: 4s;
}

@keyframes glowPulse {
    0% { opacity: 0.1; transform: scale(1); }
    100% { opacity: 0.25; transform: scale(1.2); }
}

.homepage-content {
    position: relative;
    z-index: 1;
    text-align: center;
    max-width: 720px;
    padding: 0 24px;
}

.homepage-badge {
    display: inline-block;
    padding: 6px 16px;
    border-radius: 20px;
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    font-size: 12px;
    font-weight: 500;
    color: var(--text-secondary);
    letter-spacing: 0.02em;
    margin-bottom: 24px;
}

.homepage-title {
    font-size: 4rem;
    font-weight: 800;
    line-height: 1.1;
    color: var(--text-primary);
    letter-spacing: -0.03em;
    margin-bottom: 20px;
}

.homepage-title-accent {
    background: linear-gradient(135deg, var(--accent) 0%, #a855f7 50%, var(--success) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.homepage-subtitle {
    font-size: 1.15rem;
    color: var(--text-secondary);
    line-height: 1.7;
    max-width: 560px;
    margin: 0 auto 32px;
}

.homepage-stats {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 24px;
    margin-bottom: 36px;
}

.homepage-stat {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2px;
}

.homepage-stat-number {
    font-size: 2rem;
    font-weight: 800;
    color: var(--text-primary);
    font-family: var(--font-mono);
}

.homepage-stat-label {
    font-size: 12px;
    color: var(--text-tertiary);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.homepage-stat-divider {
    width: 1px;
    height: 40px;
    background: var(--border-primary);
}

.homepage-actions {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
    margin-bottom: 40px;
}

.homepage-btn-primary {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 14px 28px;
    border-radius: var(--radius-md);
    border: none;
    background: var(--accent);
    color: white;
    font-family: var(--font-sans);
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 0 0 20px var(--accent-subtle);
    text-decoration: none;
}

.homepage-btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
    box-shadow: 0 4px 24px var(--accent-subtle);
}

.homepage-btn-secondary {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 14px 24px;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-primary);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 15px;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
}

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

.homepage-topics {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 8px;
}

.homepage-topic {
    display: inline-block;
    padding: 4px 12px;
    border-radius: 6px;
    font-size: 12px;
    font-weight: 500;
    color: var(--text-tertiary);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-secondary);
    transition: all var(--transition-fast);
}

.homepage-topic:hover {
    color: var(--accent);
    border-color: var(--accent);
}

/* Homepage Features Section */
.homepage-features {
    position: relative;
    z-index: 1;
    padding: 80px 32px;
    max-width: 1000px;
    margin: 0 auto;
}

.homepage-features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 20px;
}

.homepage-feature-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: calc(var(--radius-md) + 2px);
    padding: 28px 24px;
    text-align: center;
    transition: all var(--transition-fast);
}

.homepage-feature-card:hover {
    border-color: color-mix(in srgb, var(--border-primary) 50%, var(--accent));
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.homepage-feature-icon {
    font-size: 32px;
    margin-bottom: 12px;
}

.homepage-feature-card h3 {
    font-size: 16px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.homepage-feature-card p {
    font-size: 13px;
    color: var(--text-secondary);
    line-height: 1.6;
    margin: 0;
}

/* Homepage Footer */
.homepage-footer {
    position: relative;
    z-index: 1;
    text-align: center;
    padding: 32px;
    border-top: 1px solid var(--border-secondary);
    font-size: 13px;
    color: var(--text-tertiary);
}

.homepage-footer a {
    color: var(--text-link);
    text-decoration: none;
    font-weight: 500;
}

.homepage-footer a:hover {
    text-decoration: underline;
}

/* Homepage animations */
.animate-fade-in {
    opacity: 0;
    animation: homeFadeIn 0.6s ease forwards;
}

.animate-fade-in-up {
    opacity: 0;
    transform: translateY(20px);
    animation: homeFadeInUp 0.6s ease forwards;
}

.delay-1 { animation-delay: 0.15s; }
.delay-2 { animation-delay: 0.3s; }
.delay-3 { animation-delay: 0.45s; }
.delay-4 { animation-delay: 0.6s; }

@keyframes homeFadeIn {
    to { opacity: 1; }
}

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

/* ===================================
   MERMAID DIAGRAMS
   =================================== */

.mermaid-diagram {
    margin: 20px 0;
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    overflow: hidden;
    background: var(--bg-secondary);
}

.mermaid-diagram-header {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 16px;
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border-secondary);
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.mermaid-diagram-header .diagram-icon {
    font-size: 1rem;
}

.mermaid-diagram-header .diagram-type-badge {
    display: inline-flex;
    padding: 2px 8px;
    border-radius: 999px;
    font-size: 0.68rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    background: var(--accent-subtle);
    color: var(--accent);
    margin-left: auto;
}

.mermaid-display {
    padding: 24px 16px;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 120px;
    overflow-x: auto;
}

.mermaid-display svg {
    max-width: 100%;
    height: auto;
}

.mermaid-code {
    display: none;
}

/* ===================================
   FULL-TEXT SEARCH RESULTS
   =================================== */
.search-kbd {
    position: absolute;
    right: 8px;
    font-family: var(--font-sans);
    font-size: 10px;
    font-weight: 500;
    padding: 2px 6px;
    border-radius: 4px;
    border: 1px solid var(--border-primary);
    background: var(--bg-tertiary);
    color: var(--text-tertiary);
    pointer-events: none;
    line-height: 1.4;
}

.search-results {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    z-index: 999;
    margin-top: 4px;
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    max-height: 440px;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.search-results[hidden] {
    display: none;
}

.search-results-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 8px 12px;
    border-bottom: 1px solid var(--border-secondary);
    flex-shrink: 0;
}

.search-results-count {
    font-size: 11px;
    font-weight: 500;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.search-results-close {
    background: none;
    border: none;
    color: var(--text-tertiary);
    cursor: pointer;
    font-size: 18px;
    line-height: 1;
    padding: 0 2px;
    border-radius: var(--radius-sm);
    transition: color var(--transition-fast);
}

.search-results-close:hover {
    color: var(--text-primary);
}

.search-results-list {
    overflow-y: auto;
    overscroll-behavior: contain;
    padding: 4px;
}

.search-result-item {
    display: block;
    padding: 8px 10px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: background var(--transition-fast);
    border: none;
    background: none;
    width: 100%;
    text-align: left;
    font-family: var(--font-sans);
}

.search-result-item:hover,
.search-result-item:focus {
    background: var(--bg-hover);
    outline: none;
}

.search-result-item-title {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 13px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 2px;
}

.search-result-item-part {
    font-size: 10px;
    font-weight: 500;
    color: var(--accent);
    background: var(--accent-subtle);
    padding: 1px 6px;
    border-radius: 999px;
    flex-shrink: 0;
}

.search-result-item-snippet {
    font-size: 12px;
    color: var(--text-secondary);
    line-height: 1.5;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.search-result-item-snippet mark {
    background: var(--warning-subtle);
    color: var(--warning);
    border-radius: 2px;
    padding: 0 1px;
    font-weight: 600;
}

.search-no-results {
    padding: 24px 12px;
    text-align: center;
    color: var(--text-tertiary);
    font-size: 13px;
}

/* ===================================
   FLOATING TABLE OF CONTENTS
   =================================== */
.content-layout {
    display: flex;
    align-items: flex-start;
    gap: 24px;
    max-width: calc(var(--content-max-width) + 240px);
    margin: 0 auto;
}

.content-layout .content-wrapper {
    flex: 1;
    min-width: 0;
    max-width: var(--content-max-width);
}

.chapter-toc {
    position: sticky;
    top: calc(var(--topbar-height) + 32px);
    width: 200px;
    flex-shrink: 0;
    max-height: calc(100vh - var(--topbar-height) - 64px);
    overflow-y: auto;
    display: none;
    scrollbar-width: thin;
}

.chapter-toc-header {
    font-size: 11px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-tertiary);
    margin-bottom: 10px;
    padding-left: 12px;
}

.chapter-toc-nav {
    display: flex;
    flex-direction: column;
    border-left: 2px solid var(--border-secondary);
}

.chapter-toc-link {
    display: block;
    padding: 4px 12px;
    margin-left: -2px;
    font-size: 12px;
    font-weight: 400;
    color: var(--text-tertiary);
    text-decoration: none;
    border-left: 2px solid transparent;
    transition: all var(--transition-fast);
    line-height: 1.4;
    cursor: pointer;
}

.chapter-toc-link:hover {
    color: var(--text-secondary);
}

.chapter-toc-link.active {
    color: var(--accent);
    border-left-color: var(--accent);
    font-weight: 500;
}

.chapter-toc-link.toc-h3 {
    padding-left: 24px;
    font-size: 11px;
}

/* Show TOC on wide screens */
@media (min-width: 1200px) {
    .chapter-toc {
        display: block;
    }
}

/* ===================================
   QUIZ MODE
   =================================== */
.quiz-section {
    margin-top: 40px;
    padding-top: 32px;
    border-top: 2px solid var(--border-secondary);
}

.quiz-section-header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 20px;
}

.quiz-section-title {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--text-primary);
}

.quiz-section-badge {
    font-size: 11px;
    font-weight: 600;
    padding: 2px 8px;
    border-radius: 999px;
    background: var(--accent-subtle);
    color: var(--accent);
}

.quiz-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    padding: 20px;
    margin-bottom: 16px;
    transition: border-color var(--transition-fast);
}

.quiz-card.answered-correct {
    border-color: var(--success);
}

.quiz-card.answered-wrong {
    border-color: #f85149;
}

.quiz-question-number {
    font-size: 11px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: var(--text-tertiary);
    margin-bottom: 8px;
}

.quiz-question-text {
    font-size: 15px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 16px;
    line-height: 1.5;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.quiz-option {
    display: flex;
    align-items: flex-start;
    gap: 10px;
    padding: 10px 14px;
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-sm);
    background: var(--bg-primary);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-family: var(--font-sans);
    font-size: 13px;
    color: var(--text-secondary);
    text-align: left;
    width: 100%;
    line-height: 1.45;
}

.quiz-option:hover:not(.disabled) {
    border-color: var(--accent);
    background: var(--accent-subtle);
    color: var(--text-primary);
}

.quiz-option.disabled {
    cursor: default;
}

.quiz-option-marker {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 22px;
    height: 22px;
    flex-shrink: 0;
    border-radius: 50%;
    border: 2px solid var(--border-primary);
    font-size: 11px;
    font-weight: 700;
    color: var(--text-tertiary);
    transition: all var(--transition-fast);
}

.quiz-option:hover:not(.disabled) .quiz-option-marker {
    border-color: var(--accent);
    color: var(--accent);
}

.quiz-option.selected {
    border-color: var(--accent);
    background: var(--accent-subtle);
}

.quiz-option.selected .quiz-option-marker {
    background: var(--accent);
    border-color: var(--accent);
    color: white;
}

.quiz-option.correct {
    border-color: var(--success);
    background: var(--success-subtle);
}

.quiz-option.correct .quiz-option-marker {
    background: var(--success);
    border-color: var(--success);
    color: white;
}

.quiz-option.wrong {
    border-color: #f85149;
    background: #f8514922;
}

.quiz-option.wrong .quiz-option-marker {
    background: #f85149;
    border-color: #f85149;
    color: white;
}

.quiz-explanation {
    margin-top: 12px;
    padding: 12px 14px;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    border-left: 3px solid var(--accent);
    font-size: 13px;
    color: var(--text-secondary);
    line-height: 1.5;
    display: none;
}

.quiz-explanation.visible {
    display: block;
}

.quiz-score {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px 18px;
    background: var(--bg-secondary);
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-md);
    margin-top: 16px;
}

.quiz-score-label {
    font-size: 13px;
    font-weight: 500;
    color: var(--text-secondary);
}

.quiz-score-value {
    font-size: 15px;
    font-weight: 700;
    color: var(--accent);
}

.quiz-score-bar {
    flex: 1;
    height: 6px;
    background: var(--bg-tertiary);
    border-radius: 3px;
    overflow: hidden;
}

.quiz-score-fill {
    height: 100%;
    background: var(--accent);
    border-radius: 3px;
    transition: width 0.4s ease;
}

.quiz-reset-btn {
    padding: 6px 14px;
    border: 1px solid var(--border-primary);
    border-radius: var(--radius-sm);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 12px;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    flex-shrink: 0;
}

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

/* ===================================
   RESPONSIVE DESIGN
   =================================== */

/* Tablets and small desktops */
@media (max-width: 1024px) {
    .sidebar {
        transform: translateX(-100%);
    }

    .sidebar.open {
        transform: translateX(0);
        box-shadow: var(--shadow-lg);
    }

    .sidebar-close {
        display: flex;
    }

    .main-content {
        margin-left: 0;
    }

    .menu-toggle {
        display: flex;
    }

    .content-area {
        padding: 24px 20px 48px;
    }
}

/* Mobile */
@media (max-width: 640px) {
    html {
        font-size: 15px;
    }

    .sidebar {
        width: 85vw;
        max-width: 320px;
    }

    .topbar {
        padding: 0 16px;
        height: 48px;
    }

    .btn-mark-complete span {
        display: none;
    }

    .btn-mark-complete {
        padding: 6px 8px;
    }

    .btn-notes-toggle span {
        display: none;
    }

    .btn-notes-toggle {
        padding: 6px 8px;
    }

    .content-area {
        padding: 20px 16px 40px;
    }

    .chapter-content h1 {
        font-size: 1.6rem;
    }

    .chapter-content h2 {
        font-size: 1.3rem;
    }

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

    .chapter-nav-btn {
        max-width: 100%;
    }

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

    .back-to-top {
        bottom: 16px;
        right: 16px;
    }

    /* Homepage responsive */
    .homepage-nav {
        padding: 12px 16px;
    }

    .homepage-nav-logo span:not(.logo-icon) {
        display: none;
    }

    .homepage-title {
        font-size: 2.4rem;
    }

    .homepage-subtitle {
        font-size: 1rem;
    }

    .homepage-stats {
        gap: 16px;
    }

    .homepage-stat-number {
        font-size: 1.5rem;
    }

    .homepage-actions {
        flex-direction: column;
    }

    .homepage-btn-primary,
    .homepage-btn-secondary {
        width: 100%;
        justify-content: center;
    }

    .homepage-features {
        padding: 48px 16px;
    }

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

    .shadcn-comparison-grid {
        grid-template-columns: 1fr;
    }

    .shadcn-tabs-list {
        flex-wrap: wrap;
    }
}

/* Large screens */
@media (min-width: 1400px) {
    .content-area {
        padding: 40px 60px 80px;
    }

    .content-wrapper {
        max-width: 900px;
    }

    .content-layout {
        max-width: calc(900px + 240px);
    }
}

/* Print */
@media print {
    .sidebar, .topbar, .back-to-top, .chapter-nav, .lightbox, .notes-panel, .homepage-nav, .chapter-toc, .quiz-section {
        display: none !important;
    }
    .main-content {
        margin-left: 0;
    }
}