/**
 * Full Stack Course Template - Shared Styles
 *
 * This provides the unified styling for all courses including:
 * - Collapsible sidebar (50px → 280px on hover)
 * - Sticky positioning for sidebar
 * - Navigation styles
 * - Card and widget styles
 * - Quiz system
 * - Info/warning boxes
 * - Code blocks
 * - Responsive design
 *
 * Include after shared.css and before course-specific styles.
 */

/* =====================================================
   CSS VARIABLES - Override these in course-specific CSS
   ===================================================== */
:root {
    /* Core colors - can be overridden per course */
    --course-bg-primary: #0a0a0f;
    --course-bg-secondary: #12121a;
    --course-bg-card: #16161f;
    --course-bg-code: #0d0d12;
    --course-border: #2a2a3a;
    --course-text-primary: #f0f0f5;
    --course-text-secondary: #a0a0b8;
    --course-text-muted: #6a6a7a;
    --course-accent: #00ff41;
    --course-accent-secondary: #00cc33;
    --course-accent-orange: #d29922;
    --course-accent-red: #f85149;
    --course-accent-purple: #a371f7;

    /* Layout */
    --sidebar-collapsed: 50px;
    --sidebar-expanded: 280px;
    --content-max-width: 65ch;
    --header-height: auto;
}

/* =====================================================
   BASE RESET & TYPOGRAPHY
   ===================================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

::-webkit-scrollbar {
    width: 10px;
    height: 10px;
}

::-webkit-scrollbar-track {
    background: var(--course-bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: #3a3a4a;
    border-radius: 5px;
}

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

body {
    font-family: 'DM Sans', 'Inter', system-ui, sans-serif;
    background: var(--course-bg-primary);
    color: var(--course-text-primary);
    min-height: 100vh;
    line-height: 1.7;
}

#app-header {
    position: relative;
    z-index: 20;
}

a {
    color: var(--course-accent-secondary);
    text-decoration: none;
}

a:hover {
    color: var(--course-accent);
    text-decoration: underline;
}

/* =====================================================
   GRID BACKGROUND (optional decorative element)
   ===================================================== */
.grid-bg {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image:
        linear-gradient(var(--course-border) 1px, transparent 1px),
        linear-gradient(90deg, var(--course-border) 1px, transparent 1px);
    background-size: 60px 60px;
    opacity: 0.08;
    pointer-events: none;
    z-index: -1;
}

/* =====================================================
   HEADER
   ===================================================== */
header {
    position: relative;
    padding: 1.5rem 2rem;
    border-bottom: 1px solid var(--course-border);
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: var(--course-bg-secondary);
}

.back-link {
    color: var(--course-text-muted);
    text-decoration: none;
    font-size: 0.9rem;
    transition: color 0.15s;
}

.back-link:hover {
    color: var(--course-accent);
    text-decoration: none;
}

.header-brand h1 {
    font-size: 2rem;
    font-weight: 600;
    margin: 0;
    line-height: 1;
}

.header-brand h1 span {
    color: var(--course-accent);
}

.tagline {
    color: var(--course-text-secondary);
    font-size: 0.85rem;
    margin: 0.25rem 0 0 0;
}

/* Header auth section */
.header-auth {
    flex-shrink: 0;
    visibility: hidden;
}

.header-auth.ready {
    visibility: visible;
}

.progress-warning {
    display: flex;
    flex-direction: column;
    font-family: inherit;
    font-size: inherit;
    align-items: flex-end;
    gap: 0.15rem;
    background: rgba(251, 191, 36, 0.1);
    border: 1px solid rgba(251, 191, 36, 0.3);
    border-radius: 6px;
    padding: 0.5rem 0.75rem;
    font-size: 0.75rem;
    color: #fbbf24;
    cursor: pointer;
    transition: all 0.2s;
    text-align: right;
}

.progress-warning:hover {
    background: rgba(251, 191, 36, 0.15);
    border-color: rgba(251, 191, 36, 0.5);
}

.progress-warning-line1 {
    white-space: nowrap;
}

.progress-warning-cta {
    color: var(--course-accent);
    font-weight: 500;
    font-size: 0.8rem;
}

#progress-summary {
    display: none;
    color: var(--course-accent-secondary);
}

/* =====================================================
   PAGE LAYOUT
   ===================================================== */
.page-layout {
    display: flex;
    min-height: calc(100vh - 120px);
}

/* =====================================================
   COLLAPSIBLE SIDEBAR
   ===================================================== */
#sidebar-nav {
    width: var(--sidebar-collapsed);
    flex-shrink: 0;
    background: var(--course-bg-secondary);
    border-right: 1px solid var(--course-border);
    position: sticky;
    top: 0;
    height: 100vh;
    overflow: hidden;
    padding: 1rem 0;
    transition: width 0.25s ease;
    z-index: 100;
}

#sidebar-nav:hover,
#sidebar-nav:focus-within,
body.browser-find-active #sidebar-nav {
    width: var(--sidebar-expanded);
    overflow-y: auto;
    overscroll-behavior: contain;   /* don't chain/stall scroll at the sidebar's ends */
}

/* Nav items hidden when collapsed */
#sidebar-nav .nav-topic,
#sidebar-nav .nav-subtopic,
#sidebar-nav .nav-section,
#sidebar-nav .nav-part {
    opacity: 0;
    transition: opacity 0.15s ease;
    white-space: nowrap;
}

#sidebar-nav:hover .nav-topic,
#sidebar-nav:hover .nav-subtopic,
#sidebar-nav:hover .nav-section,
#sidebar-nav:hover .nav-part,
#sidebar-nav:focus-within .nav-topic,
#sidebar-nav:focus-within .nav-subtopic,
#sidebar-nav:focus-within .nav-section,
#sidebar-nav:focus-within .nav-part,
body.browser-find-active #sidebar-nav .nav-topic,
body.browser-find-active #sidebar-nav .nav-subtopic,
body.browser-find-active #sidebar-nav .nav-section,
body.browser-find-active #sidebar-nav .nav-part {
    opacity: 1;
}

/* =====================================================
   NAVIGATION ITEMS
   ===================================================== */
.nav-part {
    margin-bottom: 1.5rem;
}

.nav-part-title {
    padding: 0.5rem 1rem;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--course-text-muted);
}

/* Course-declared cross-links (course.related) under the section list */
.nav-related {
    margin-top: 1.5rem;
    padding-top: 0.75rem;
    border-top: 1px solid var(--course-border);
}

.nav-topic {
    padding: 0.75rem 1rem;
    border-left: 3px solid transparent;
    transition: all 0.15s;
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    flex-wrap: wrap;
}

.nav-topic-title {
    font-weight: 600;
    font-size: 0.9rem;
    color: var(--course-text-primary);
    margin-bottom: 0.3rem;
    flex: 1;
}

.nav-topic.active .nav-topic-title {
    color: var(--course-accent);
}

.nav-keywords {
    display: flex;
    flex-wrap: wrap;
    gap: 0.3rem;
}

.nav-keyword {
    font-size: 0.65rem;
    color: var(--course-text-secondary);
    background: rgba(255, 255, 255, 0.05);
    padding: 0.15rem 0.4rem;
    border-radius: 3px;
}

.nav-subtopic {
    padding: 0.4rem 1rem 0.4rem 1.75rem;
    cursor: pointer;
    border-left: 2px solid transparent;
    transition: all 0.15s;
    font-size: 0.8rem;
    color: var(--course-text-secondary);
    display: flex;
    align-items: center;
}

.nav-subtopic:hover {
    background: rgba(255, 255, 255, 0.03);
    color: var(--course-text-primary);
}

.nav-subtopic.active {
    background: rgba(0, 255, 65, 0.03);
    border-left-color: var(--course-accent-secondary);
    color: var(--course-accent-secondary);
}

.nav-subtopic::before {
    content: "\2514"; /* └ */
    margin-right: 0.5rem;
    opacity: 0.4;
    flex-shrink: 0;
}

/* Let the label take the remaining width and truncate, so a long title can't
   push the mastery badge off the edge of the fixed-width sidebar. Full title
   stays available via the title="" tooltip set in navigation.js. */
.nav-subtopic-text {
    flex: 1;
    min-width: 0;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

/* Simple nav section style */
.nav-section {
    display: block;
    padding: 0.6rem 1rem;
    color: var(--course-text-secondary);
    text-decoration: none;
    font-size: 0.85rem;
    border-left: 2px solid transparent;
    transition: all 0.15s;
    cursor: pointer;
}

.nav-section:hover {
    background: rgba(255, 255, 255, 0.03);
    color: var(--course-text-primary);
    text-decoration: none;
}

.nav-section.active {
    background: rgba(0, 255, 65, 0.03);
    color: var(--course-accent);
    border-left-color: var(--course-accent);
}

.nav-section.completed {
    color: var(--course-accent);
}

.nav-section.completed::before {
    content: "\2713 "; /* ✓ */
}

.nav-section.locked {
    color: var(--course-text-muted);
    cursor: not-allowed;
}

.nav-section .icon {
    margin-right: 0.5rem;
}

/* Mastery indicators */
.mastery-indicator {
    font-size: 0.7rem;
    font-weight: 600;
    padding: 0.1rem 0.4rem;
    border-radius: 4px;
    margin-left: 0.5rem;
    font-family: 'JetBrains Mono', monospace;
    white-space: nowrap;
    flex-shrink: 0;
}

.mastery-partial .mastery-indicator {
    background: rgba(251, 191, 36, 0.2);
    color: #fbbf24;
}

.mastery-almost .mastery-indicator {
    background: rgba(0, 212, 170, 0.2);
    color: var(--course-accent-secondary);
}

.mastery-complete .mastery-indicator {
    background: rgba(0, 255, 65, 0.2);
    color: var(--course-accent);
}

/* =====================================================
   MAIN CONTENT AREA
   ===================================================== */
main {
    flex: 1;
    max-width: 1400px;
    padding: 2rem 3rem;
    min-width: 0;
}

/* Content width constraints for readability */
main p,
main ul,
main ol,
main h3,
main .lesson-intro,
main .info-box,
main .warning-box,
main .story-box {
    max-width: var(--content-max-width);
}

main p {
    margin-bottom: 1.5rem;
}

main p:last-child {
    margin-bottom: 0;
}

main ul li,
main ol li {
    margin-bottom: 0.75rem;
}

main ul li:last-child,
main ol li:last-child {
    margin-bottom: 1.5rem;
}

/* =====================================================
   SECTIONS
   ===================================================== */
/* Scoped to the renderer's page sections (direct children of #course-root):
   a bare `section` selector also swallowed <section> elements that widgets
   create elsewhere in the page (e.g. the anatomy lightbox's tab panels),
   force-hiding them. Only course page sections participate in show/hide. */
#course-root > section {
    display: none;
    animation: fadeIn 0.3s ease;
}

#course-root > section.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* =====================================================
   CARDS
   ===================================================== */
.card {
    background: var(--course-bg-card);
    border: 1px solid var(--course-border);
    padding: 2rem;
    margin-bottom: 1.5rem;
    border-radius: 0;
}

h2 {
    font-size: 1.6rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

h2 .icon {
    width: 34px;
    height: 34px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--course-accent);
    color: var(--course-bg-primary);
    font-size: 0.9rem;
    font-family: 'JetBrains Mono', monospace;
    border-radius: 0;
}

.lesson-intro {
    color: var(--course-text-secondary);
    font-size: 0.95rem;
    margin-bottom: 1.5rem;
    line-height: 1.7;
}

.lesson-intro p {
    margin-bottom: 1rem;
}

.lesson-intro p:last-child {
    margin-bottom: 0;
}

/* =====================================================
   CODE BLOCKS
   ===================================================== */
code {
    background: rgba(0, 255, 65, 0.08);
    border: 1px solid rgba(0, 255, 65, 0.2);
    padding: 0.1rem 0.35rem;
    border-radius: 4px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85em;
    color: var(--course-accent);
}

pre {
    background: var(--course-bg-code);
    border: 1px solid var(--course-border);
    border-radius: 8px;
    padding: 16px;
    overflow-x: auto;
    margin: 16px 0;
}

pre code {
    background: none;
    border: none;
    padding: 0;
    margin: 0;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.875rem;
    line-height: 1.5;
    color: var(--course-text-primary);
    display: block;
    white-space: pre;
}

/* =====================================================
   INFO & WARNING BOXES
   ===================================================== */
.info-box {
    background: linear-gradient(135deg, rgba(0, 212, 170, 0.08), transparent);
    border-left: 2px solid var(--course-accent-secondary);
    padding: 1rem 1.25rem;
    margin-top: 1.5rem;
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
    color: var(--course-text-secondary);
    border-radius: 0;
}

.info-box strong {
    color: var(--course-accent-secondary);
}

.warning-box {
    background: linear-gradient(135deg, rgba(210, 153, 34, 0.08), transparent);
    border-left: 2px solid var(--course-accent-orange);
    padding: 1rem 1.25rem;
    margin-top: 1.5rem;
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
    color: var(--course-text-secondary);
    border-radius: 0;
}

.warning-box strong {
    color: var(--course-accent-orange);
}

.story-box {
    background: linear-gradient(135deg, rgba(251, 191, 36, 0.08), transparent);
    border-left: 2px solid #fbbf24;
    padding: 1rem 1.25rem;
    margin-top: 1.5rem;
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
    color: var(--course-text-secondary);
}

.story-box strong {
    color: #fbbf24;
}

/* =====================================================
   WIDGETS (base styles)
   ===================================================== */
.widget {
    background: var(--course-bg-code);
    border: 1px solid var(--course-border);
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

.widget-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--course-accent-secondary);
    margin-bottom: 1rem;
    text-align: center;
}

/* =====================================================
   QUIZ SYSTEM
   ===================================================== */
.quiz {
    margin-top: 1.5rem;
    padding: 1.25rem;
    background: var(--course-bg-secondary);
    border: 1px solid var(--course-border);
    border-radius: 8px;
    max-width: var(--content-max-width);
}

.quiz-title {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--course-accent-secondary);
    margin-bottom: 1rem;
}

.quiz-question {
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--course-text-primary);
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.quiz-option {
    display: flex;
    align-items: center;
    padding: 0.75rem 1rem;
    background: var(--course-bg-code);
    border: 1px solid var(--course-border);
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.15s;
}

.quiz-option:hover {
    border-color: var(--course-accent-secondary);
}

.quiz-option.selected {
    border-color: var(--course-accent);
    background: rgba(0, 255, 65, 0.05);
}

.quiz-option.correct {
    border-color: #4ade80;
    background: rgba(74, 222, 128, 0.1);
}

.quiz-option.incorrect {
    border-color: #f87171;
    background: rgba(248, 113, 113, 0.1);
}

.quiz-option input {
    display: none;
}

.quiz-option .letter {
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--course-border);
    border-radius: 4px;
    margin-right: 0.75rem;
    font-size: 0.8rem;
    font-weight: 600;
    flex-shrink: 0;
}

.quiz-option.selected .letter {
    background: var(--course-accent);
    color: #000;
}

.quiz-option.correct .letter {
    background: #4ade80;
    color: #000;
}

.quiz-option.incorrect .letter {
    background: #f87171;
    color: #000;
}

.quiz-check,
.quiz-submit {
    margin-top: 1rem;
    padding: 0.6rem 1.5rem;
    background: var(--course-accent);
    color: #000;
    border: none;
    border-radius: 6px;
    font-weight: 600;
    cursor: pointer;
    transition: filter 0.15s;
}

.quiz-check:hover,
.quiz-submit:hover {
    filter: brightness(1.1);
}

.quiz-check:disabled,
.quiz-submit:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.quiz-feedback {
    margin-top: 1rem;
    padding: 0.75rem 1rem;
    border-radius: 6px;
    font-size: 0.9rem;
}

.quiz-feedback.correct {
    background: rgba(74, 222, 128, 0.1);
    border: 1px solid #4ade80;
    color: #4ade80;
}

.quiz-feedback.incorrect {
    background: rgba(248, 113, 113, 0.1);
    border: 1px solid #f87171;
    color: #f87171;
}

/* =====================================================
   EXPANDABLE SECTIONS
   ===================================================== */
.expand-section,
details.expand-section {
    margin-top: 1rem;
    border: 1px solid var(--course-border);
    border-radius: 6px;
    overflow: hidden;
}

.expand-section summary {
    padding: 0.75rem 1rem;
    background: var(--course-bg-secondary);
    cursor: pointer;
    font-weight: 500;
    color: var(--course-text-secondary);
    transition: all 0.15s;
    list-style: none;
}

.expand-section summary::-webkit-details-marker {
    display: none;
}

.expand-section summary::before {
    content: "\25B6"; /* ▶ */
    display: inline-block;
    margin-right: 0.5rem;
    transition: transform 0.15s;
    font-size: 0.75rem;
}

.expand-section[open] summary::before {
    transform: rotate(90deg);
}

.expand-section summary:hover {
    background: var(--course-bg-card);
    color: var(--course-text-primary);
}

.expand-content {
    padding: 1rem;
    background: var(--course-bg-card);
}

/* =====================================================
   ACHIEVEMENTS / CHALLENGES
   ===================================================== */
.achievements {
    margin-top: 1.5rem;
    padding: 1rem;
    background: rgba(0, 212, 170, 0.05);
    border-radius: 8px;
    border: 1px solid rgba(0, 212, 170, 0.2);
    max-width: var(--content-max-width);
}

.achievements-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--course-accent);
    margin-bottom: 1rem;
}

.achievement-list {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 0.75rem;
}

.achievement {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.75rem;
    background: var(--course-bg-secondary);
    border-radius: 6px;
    border: 1px solid var(--course-border);
    cursor: help;
    transition: all 0.2s;
}

.achievement.unlocked {
    border-color: var(--course-accent);
    background: rgba(0, 212, 170, 0.1);
}

.achievement-icon {
    font-size: 1.2rem;
    opacity: 0.5;
}

.achievement.unlocked .achievement-icon {
    opacity: 1;
}

.achievement-name {
    font-weight: 600;
    font-size: 0.85rem;
    color: var(--course-text-primary);
}

.achievement-desc {
    font-size: 0.75rem;
    color: var(--course-text-secondary);
    flex: 1;
}

/* =====================================================
   AUTH MODAL
   ===================================================== */
.auth-modal {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
}

.auth-modal-backdrop {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.8);
}

.auth-modal-content {
    position: relative;
    background: var(--course-bg-secondary);
    border: 1px solid var(--course-border);
    border-radius: 12px;
    padding: 2rem;
    width: 90%;
    max-width: 400px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
}

.auth-modal-close {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    color: var(--course-text-secondary);
    font-size: 1.5rem;
    cursor: pointer;
    line-height: 1;
    padding: 0;
}

.auth-modal-close:hover {
    color: var(--course-text-primary);
}

.auth-modal-content h2 {
    margin: 0 0 0.25rem 0;
    color: var(--course-accent);
    font-size: 1.5rem;
}

.auth-modal-subtitle {
    margin: 0 0 1.5rem 0;
    color: var(--course-text-secondary);
    font-size: 0.9rem;
}

.auth-modal-toggle {
    margin-top: 1.5rem;
    text-align: center;
    font-size: 0.85rem;
    color: var(--course-text-secondary);
}

.auth-modal-toggle button {
    background: none;
    border: none;
    color: var(--course-accent-secondary);
    cursor: pointer;
    text-decoration: underline;
    font-size: inherit;
}

/* Auth form overrides to match course theme */
.auth-form-group label {
    color: var(--course-accent-secondary);
}

.auth-form-group input[type="email"],
.auth-form-group input[type="password"],
.auth-form-group input[type="text"] {
    background: var(--course-bg-primary);
    border: 1px solid var(--course-border);
    color: var(--course-text-primary);
}

.auth-form-group input::placeholder {
    color: var(--course-text-secondary);
}

.auth-form-group input:focus {
    border-color: var(--course-accent-secondary);
    background: var(--course-bg-primary);
}

.auth-password-toggle {
    color: var(--course-text-secondary);
}

.auth-password-toggle:hover {
    color: var(--course-accent-secondary);
}

.auth-submit-btn {
    border: 1px solid var(--course-border);
    color: var(--course-accent);
    background: transparent;
}

.auth-submit-btn:hover {
    border-color: var(--course-accent);
    color: var(--course-accent);
}

/* =====================================================
   PAGE CHAT ASSISTANT
   ===================================================== */
#page-chat-root {
    position: fixed;
    right: 16px;
    bottom: 36px;
    z-index: 35;
}

.page-chat-launcher {
    display: flex;
    flex-direction: column;
    gap: 0.1rem;
    min-width: 180px;
    padding: 0.8rem 1rem;
    border: 1px solid color-mix(in srgb, var(--course-accent) 45%, var(--course-border));
    border-radius: 16px;
    background:
        linear-gradient(135deg, color-mix(in srgb, var(--course-accent) 16%, transparent), transparent 60%),
        var(--course-bg-card);
    color: var(--course-text-primary);
    cursor: pointer;
    box-shadow: 0 16px 50px rgba(0, 0, 0, 0.35);
    text-align: left;
    transition: opacity 0.18s ease, transform 0.18s ease, border-color 0.15s ease;
}

.page-chat-launcher:hover {
    border-color: var(--course-accent);
    transform: translateY(-1px);
}

.page-chat-launcher-title {
    font-size: 0.95rem;
    font-weight: 600;
}

.page-chat-launcher-subtitle {
    font-size: 0.78rem;
    color: var(--course-text-secondary);
}

.page-chat-overlay {
    position: fixed;
    inset: 0;
    background: rgba(5, 8, 14, 0.55);
    backdrop-filter: blur(3px);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.18s ease;
}

.page-chat-panel {
    position: fixed;
    top: 88px;
    right: 16px;
    width: min(420px, calc(100vw - 32px));
    height: min(720px, calc(100vh - 120px));
    display: flex;
    flex-direction: column;
    border: 1px solid var(--course-border);
    border-radius: 24px;
    background:
        radial-gradient(circle at top right, color-mix(in srgb, var(--course-accent) 15%, transparent), transparent 35%),
        linear-gradient(180deg, color-mix(in srgb, var(--course-bg-card) 92%, black), var(--course-bg-secondary));
    box-shadow: 0 30px 80px rgba(0, 0, 0, 0.45);
    overflow: hidden;
    opacity: 0;
    pointer-events: none;
    transform: translateY(12px) scale(0.98);
    transition: opacity 0.18s ease, transform 0.18s ease;
}

#page-chat-root.open .page-chat-panel {
    opacity: 1;
    pointer-events: auto;
    transform: translateY(0) scale(1);
}

#page-chat-root.open .page-chat-overlay,
#page-chat-root.closing .page-chat-overlay {
    opacity: 1;
    pointer-events: auto;
}

#page-chat-root.open .page-chat-launcher,
#page-chat-root.closing .page-chat-launcher {
    opacity: 0;
    pointer-events: none;
    transform: translateY(8px);
}

.page-chat-header {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    padding: 1rem 1.1rem 0.9rem;
    border-bottom: 1px solid var(--course-border);
    background: color-mix(in srgb, var(--course-bg-card) 82%, black);
}

.page-chat-eyebrow {
    font-size: 0.72rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--course-accent);
    margin-bottom: 0.3rem;
}

.page-chat-header h3 {
    font-size: 1.05rem;
    line-height: 1.2;
}

.page-chat-section-label {
    margin-top: 0.25rem;
    color: var(--course-text-secondary);
    font-size: 0.82rem;
}

.page-chat-header-actions {
    display: flex;
    align-items: flex-start;
    gap: 0.45rem;
}

.page-chat-clear,
.page-chat-close,
.page-chat-send {
    border: 1px solid var(--course-border);
    background: transparent;
    color: var(--course-text-primary);
    cursor: pointer;
}

.page-chat-clear {
    padding: 0.4rem 0.7rem;
    border-radius: 999px;
    font-size: 0.8rem;
}

.page-chat-close {
    width: 34px;
    height: 34px;
    border-radius: 999px;
    font-size: 1.3rem;
    line-height: 1;
}

.page-chat-history {
    flex: 1;
    min-height: 0;
    overflow-y: auto;
    padding: 1rem 1.1rem;
    display: flex;
    flex-direction: column;
    gap: 0.85rem;
}

.page-chat-empty {
    padding: 0.95rem 1rem;
    border: 1px dashed color-mix(in srgb, var(--course-accent) 40%, var(--course-border));
    border-radius: 16px;
    background: color-mix(in srgb, var(--course-bg-secondary) 86%, black);
    color: var(--course-text-secondary);
    font-size: 0.9rem;
}

.page-chat-empty p + p {
    margin-top: 0.65rem;
}

.page-chat-message {
    max-width: 92%;
    padding: 0.8rem 0.95rem;
    border-radius: 18px;
    border: 1px solid var(--course-border);
    white-space: pre-wrap;
    word-break: break-word;
}

.page-chat-message.user {
    align-self: flex-end;
    background: color-mix(in srgb, var(--course-accent) 18%, var(--course-bg-card));
    border-color: color-mix(in srgb, var(--course-accent) 42%, var(--course-border));
}

.page-chat-message.assistant {
    align-self: flex-start;
    background: color-mix(in srgb, var(--course-bg-card) 90%, black);
}

.page-chat-message.error {
    align-self: flex-start;
    background: rgba(248, 81, 73, 0.1);
    border-color: rgba(248, 81, 73, 0.45);
}

.page-chat-message-label {
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--course-text-muted);
    margin-bottom: 0.35rem;
}

.page-chat-message-body {
    font-size: 0.94rem;
    line-height: 1.6;
}

.page-chat-progress {
    padding: 0 1rem 0.85rem;
}

.page-chat-composer {
    padding: 1rem 1.1rem 1.1rem;
    border-top: 1px solid var(--course-border);
    background: color-mix(in srgb, var(--course-bg-card) 84%, black);
}

.page-chat-composer-label {
    display: block;
    font-size: 0.75rem;
    color: var(--course-text-secondary);
    margin-bottom: 0.4rem;
}

.page-chat-input {
    width: 100%;
    min-height: 88px;
    padding: 0.85rem 0.95rem;
    border: 1px solid var(--course-border);
    border-radius: 16px;
    background: color-mix(in srgb, var(--course-bg-secondary) 88%, black);
    color: var(--course-text-primary);
    font: inherit;
    resize: vertical;
}

.page-chat-input:focus {
    outline: none;
    border-color: var(--course-accent);
    box-shadow: 0 0 0 3px color-mix(in srgb, var(--course-accent) 16%, transparent);
}

.page-chat-composer-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
    margin-top: 0.7rem;
}

.page-chat-hint {
    font-size: 0.76rem;
    color: var(--course-text-muted);
}

.page-chat-send {
    padding: 0.7rem 1rem;
    border-radius: 999px;
    background: color-mix(in srgb, var(--course-accent) 18%, var(--course-bg-card));
    border-color: color-mix(in srgb, var(--course-accent) 40%, var(--course-border));
    font-weight: 600;
}

.page-chat-send:disabled,
.page-chat-input:disabled {
    opacity: 0.65;
    cursor: not-allowed;
}


/* =====================================================
   PAGE TIMING FOOTER
   ===================================================== */
#page-timing {
    position: fixed;
    bottom: 8px;
    right: 8px;
    font-size: 11px;
    color: var(--course-text-muted);
    font-family: 'JetBrains Mono', monospace;
}

/* =====================================================
   RESPONSIVE DESIGN
   ===================================================== */
@media (max-width: 900px) {
    .page-layout {
        flex-direction: column;
    }

    #sidebar-nav {
        width: 100% !important;
        height: auto !important;
        position: relative;
        border-right: none;
        border-bottom: 1px solid var(--course-border);
        max-height: 50vh;
        overflow-y: auto !important;
    }

    #sidebar-nav::before {
        display: none;
    }

    #sidebar-nav .nav-topic,
    #sidebar-nav .nav-subtopic,
    #sidebar-nav .nav-section,
    #sidebar-nav .nav-part {
        opacity: 1 !important;
    }

    main {
        padding: 1rem;
    }

    header {
        padding: 1rem;
        flex-wrap: wrap;
        gap: 0.5rem;
    }

    .header-brand h1 {
        font-size: 1.5rem;
    }

    .card {
        padding: 1.25rem;
    }

    .quiz {
        padding: 1rem;
    }

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

    .achievement {
        flex-wrap: wrap;
        padding: 0.5rem;
        gap: 0.5rem;
    }

    .achievement-name {
        font-size: 0.8rem;
    }

    .achievement-desc {
        font-size: 0.7rem;
        width: 100%;
        margin-left: 1.75rem;
    }

    #page-chat-root {
        right: 12px;
        bottom: 20px;
    }

    .page-chat-panel {
        top: auto;
        right: 12px;
        bottom: 88px;
        height: min(680px, calc(100vh - 110px));
    }
}

@media (max-width: 600px) {
    header {
        flex-direction: column;
        align-items: flex-start;
    }

    .header-auth {
        width: 100%;
    }

    .progress-warning {
        width: 100%;
        align-items: center;
        text-align: center;
    }

    .page-chat-launcher {
        min-width: 156px;
        padding: 0.72rem 0.9rem;
    }

    .page-chat-panel {
        left: 10px;
        right: 10px;
        bottom: 10px;
        width: auto;
        height: calc(100vh - 20px);
        max-height: none;
        border-radius: 22px;
    }

    .page-chat-composer-row {
        flex-direction: column;
        align-items: stretch;
    }

    .page-chat-send {
        width: 100%;
    }
}

/* Cross-cutting callout box */
.callout{margin:18px 0 4px;padding:12px 16px;border-left:3px solid var(--course-accent,#39c5cf);background:var(--course-bg-secondary,rgba(127,127,127,0.06));border-radius:0 8px 8px 0;font-size:0.92rem;line-height:1.55;}

/* ── Course catalog (multi-course instance home) ───────────────────────────── */
.course-catalog {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.1rem;
    padding: 0.5rem 0 2rem;
}
.catalog-card {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    padding: 1.25rem 1.35rem;
    border: 1px solid var(--border, #2a2f3a);
    border-radius: 12px;
    background: var(--card-bg, #161a22);
    text-decoration: none;
    color: inherit;
    transition: border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
.catalog-card:hover {
    border-color: var(--accent, #3b82f6);
    transform: translateY(-2px);
    box-shadow: 0 6px 22px rgba(0, 0, 0, .25);
}
.catalog-card h3 {
    margin: 0;
    font-size: 1.15rem;
    color: var(--accent, #3b82f6);
}
.catalog-card .catalog-tagline {
    margin: 0;
    font-size: .92rem;
    line-height: 1.45;
    opacity: .85;
    flex: 1;
}
.catalog-card .catalog-meta {
    font-size: .8rem;
    opacity: .6;
    font-variant-numeric: tabular-nums;
}
/* Course switcher (top of the sidebar, multi-course instances): a vertical list,
   hidden while the sidebar is collapsed and revealed on expand — same behavior as
   the section nav items below it. Without this the <a>s render inline and cram. */
.course-switcher {
    display: flex;
    flex-direction: column;
    padding-bottom: .5rem;
    margin-bottom: .5rem;
    border-bottom: 1px solid var(--course-border);
}
.course-link {
    display: block;
    padding: .35rem 1rem;
    color: var(--course-text-secondary);
    text-decoration: none;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    opacity: 0;
    transition: opacity .15s ease, color .15s ease;
}
.course-link:hover { color: var(--accent, #3b82f6); text-decoration: none; }
.course-link.active { color: var(--accent, #3b82f6); font-weight: 600; }
.course-link.course-home { font-size: .82rem; opacity: 0; }
#sidebar-nav:hover .course-link,
#sidebar-nav:focus-within .course-link,
body.browser-find-active .course-link { opacity: 1; }

/* ── Catalog: per-course accent + full-width (no sidebar) home ─────────────── */
.course-catalog { max-width: 1120px; margin: 0 auto; }
.catalog-card { position: relative; overflow: hidden; }
.catalog-card::before {
    content: "";
    position: absolute;
    top: 0; left: 0; right: 0;
    height: 4px;
    background: var(--card-color, var(--accent, #3b82f6));
    opacity: .9;
}
.catalog-card:hover { border-color: var(--card-color, var(--accent, #3b82f6)); }
/* Kill the global a:hover underline on the card anchor (clashes with the accents). */
.catalog-card:hover, .catalog-card:hover h3, .catalog-card:focus { text-decoration: none; }
.catalog-card h3 { color: var(--card-color, var(--accent, #3b82f6)); }
.catalog-icon {
    font-family: "JetBrains Mono", ui-monospace, monospace;
    font-size: 1.55rem;
    font-weight: 600;
    line-height: 1;
    color: var(--card-color, var(--accent, #3b82f6));
}
/* The catalog home is full-width — the course/section sidebar has no place here. */
body.catalog-home #sidebar-nav { display: none; }
body.catalog-home .page-layout { display: block; }
body.catalog-home main { width: 100%; max-width: 100%; }

/* ── Catalog completion badges ─────────────────────────────────────────────── */
.catalog-card .catalog-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: .5rem;
}
.catalog-badge { font-size: .8rem; font-weight: 600; }
.catalog-badge.badge-done { color: #3fb950; }          /* green ✓ Complete */
.catalog-badge.badge-partial { color: var(--card-color, var(--accent, #3b82f6)); opacity: .9; }

/* ── Fail-loud: progress-not-saved banner ──────────────────────────────────── */
.save-error-bar {
    position: fixed;
    top: 0; left: 0; right: 0;
    z-index: 1000;
    background: #5c1a1a;
    color: #ffd7d7;
    border-bottom: 1px solid #f85149;
    padding: .6rem 2.5rem .6rem 1rem;
    font-size: .9rem;
    text-align: center;
}
.save-error-bar button {
    position: absolute;
    right: .6rem; top: 50%; transform: translateY(-50%);
    background: none; border: none; color: inherit;
    font-size: 1.15rem; cursor: pointer; line-height: 1;
}

/* Brand title doubles as a home/catalog link on multi-course instances. */
.brand-home { cursor: pointer; }
.brand-home:hover { opacity: .85; }

/* ── Sidebar section rows: title truncates, progress badge pinned right ─────── */
.nav-section {
    display: flex;
    align-items: center;
    gap: 0.4rem;
}
.nav-section .nav-title {
    flex: 1 1 auto;
    min-width: 0;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
.nav-section .nav-badge {
    flex: 0 0 auto;
    margin-left: auto;
    font-size: 0.72rem;
    font-weight: 600;
    font-variant-numeric: tabular-nums;
    color: var(--course-text-muted);
}
.nav-section .nav-badge.badge-complete { color: var(--course-accent); }
.nav-section.active .nav-badge { color: var(--course-accent); }

/* Grouped nav (course.topics): .nav-topic/.nav-topic-title headers (styled
   above) followed by their sections; grouped rows indent under the header. */
.nav-section.in-topic { padding-left: 1.75rem; }

/* ── Tables in course content (e.g. <table class="ref-table">) ─────────────── */
#course-root table {
    width: 100%;
    border-collapse: collapse;
    margin: 1.25rem 0;
    font-size: 0.9rem;
    background: var(--course-bg-secondary);
    border: 1px solid var(--course-border);
    border-radius: 8px;
    overflow: hidden;
}
#course-root th {
    text-align: left;
    padding: 0.6rem 0.85rem;
    background: rgba(255, 255, 255, 0.03);
    color: var(--course-accent);
    border-bottom: 2px solid var(--course-border);
    font-weight: 600;
    white-space: nowrap;
}
#course-root td {
    padding: 0.55rem 0.85rem;
    border-bottom: 1px solid var(--course-border);
    vertical-align: top;
    line-height: 1.5;
}
#course-root tbody tr:last-child td { border-bottom: none; }
#course-root tbody tr:hover td { background: rgba(255, 255, 255, 0.02); }


/* Image blocks (course memes / figures) */
.course-image {
    margin: 1.6rem 0;
    text-align: left;
    max-width: 560px;
}
.course-image img {
    max-width: 100%;
    border-radius: 12px;
    box-shadow: 0 4px 18px rgba(0, 0, 0, 0.35);
}
.course-image figcaption {
    margin-top: 0.5rem;
    font-size: 0.82rem;
    opacity: 0.65;
}

/* Diagram blocks (Mermaid -> inline SVG). The diagram is the lead artifact of a
   section, so it gets generous space and a subtle framed surface. */
.course-diagram {
    margin: 1.8rem 0;
    padding: 1.4rem 1rem;
    background:
        linear-gradient(180deg, rgba(0, 255, 65, 0.03), transparent),
        var(--course-bg-code);
    border: 1px solid var(--course-border);
    border-radius: 14px;
    text-align: center;
}
.course-diagram .mermaid-mount {
    display: flex;
    justify-content: center;
    min-height: 1.5rem;
    color: var(--course-text-secondary);
    font-size: 0.85rem;   /* styles the "Rendering diagram…" placeholder */
}
.course-diagram .mermaid-mount svg {
    /* Render near natural size. Height is the primary cap (so a tall diagram
       never dominates the screen); width is allowed to grow into the column so
       WIDE diagrams — e.g. two subgraphs Mermaid lays out side by side — aren't
       squeezed into a tiny strip. A single small max-width capped both equally,
       which over-shrank landscape diagrams. !important overrides Mermaid's
       inline max-width. Shrinks to the column on narrow screens. */
    width: auto;
    max-width: min(100%, 900px) !important;
    height: auto;
    max-height: 62vh;
}
.course-diagram figcaption {
    margin-top: 1rem;
    font-size: 0.9rem;
    color: var(--course-text-secondary);
    line-height: 1.5;
    text-align: center;
}
.course-diagram figcaption code {
    background: rgba(255, 255, 255, 0.06);
    padding: 0.05rem 0.35rem;
    border-radius: 4px;
}