:root {
    --color-bg-primary: #0f172a;
    --color-bg-secondary: #1e293b;
    --color-bg-tertiary: #334155;
    --color-border: #475569;
    --color-text-primary: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-accent: #38bdf8;
    --color-accent-hover: #0ea5e9;
    --color-success: #22c55e;
    --color-warning: #eab308;
    --color-danger: #ef4444;
    --color-robotics: #a855f7;
    --color-embedded: #f59e0b;
    --color-essential: #ec4899;
    --color-overlay: rgba(2, 6, 23, 0.76);
    --color-github-bg: #24292f;
    --color-github-hover: #32383f;
    --color-github-text: #f0f6fc;
    --color-github-border: rgba(240, 246, 252, 0.12);
    --color-github-muted: rgba(240, 246, 252, 0.78);
    --sidebar-width: 300px;
    color-scheme: dark;
}

:root[data-theme='light'] {
    --color-bg-primary: #f8fafc;
    --color-bg-secondary: #e2e8f0;
    --color-bg-tertiary: #cbd5e1;
    --color-border: #94a3b8;
    --color-text-primary: #0f172a;
    --color-text-secondary: #475569;
    --color-accent: #0284c7;
    --color-accent-hover: #0369a1;
    --color-overlay: rgba(15, 23, 42, 0.45);
    --color-github-bg: #f6f8fa;
    --color-github-hover: #eef2f6;
    --color-github-text: #24292f;
    --color-github-border: #d0d7de;
    --color-github-muted: #57606a;
    color-scheme: light;
}

:root[data-theme='dark'] {
    color-scheme: dark;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', sans-serif;
    background: var(--color-bg-primary);
    color: var(--color-text-primary);
    line-height: 1.6;
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* ══════════════════════════════════════
   HEADER
   ══════════════════════════════════════ */
.app-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 16px;
    padding: 12px 24px;
    background: var(--color-bg-secondary);
    border-bottom: 1px solid var(--color-bg-tertiary);
    flex-shrink: 0;
}

.header-left {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 16px;
}

.app-logo {
    width: 56px;
    height: 56px;
    display: grid;
    place-items: center;
    border-radius: 14px;
    background: var(--color-bg-tertiary);
    border: 1px solid var(--color-bg-tertiary);
    flex-shrink: 0;
}

.app-logo img {
    width: 100%;
    height: 100%;
    object-fit: contain;
}

.header-controls {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
}

.app-header h1 {
    font-size: 1.3rem;
    color: var(--color-accent);
}

.repo-link {
    display: inline-flex;
    align-items: center;
    padding: 6px 12px;
    gap: 8px;
    border: 1px solid var(--color-github-border);
    border-radius: 999px;
    background: var(--color-github-bg);
    color: var(--color-github-text);
    font-size: 0.85rem;
    font-weight: 600;
    text-decoration: none;
    box-shadow: 0 1px 0 rgba(1, 4, 9, 0.1);
    transition: background 0.2s, border-color 0.2s, color 0.2s, transform 0.2s, box-shadow 0.2s;
}

.repo-link::before {
    content: 'View on';
    font-size: 0.72rem;
    font-weight: 700;
    letter-spacing: 0.04em;
    text-transform: uppercase;
    color: var(--color-github-muted);
}

.repo-link:hover,
.repo-link:focus {
    background: var(--color-github-hover);
    border-color: var(--color-github-border);
    color: var(--color-github-text);
    box-shadow: 0 3px 10px rgba(1, 4, 9, 0.22);
    transform: translateY(-1px);
}

.theme-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    padding: 0;
    background: var(--color-bg-tertiary);
    color: var(--color-text-primary);
    border: 1px solid var(--color-bg-tertiary);
    border-radius: 999px;
    font-size: 1rem;
    line-height: 1;
    cursor: pointer;
    transition: border-color 0.2s, background 0.2s, color 0.2s, transform 0.2s;
}

.theme-toggle:hover,
.theme-toggle:focus {
    border-color: var(--color-accent);
    color: var(--color-accent);
    transform: translateY(-1px);
}

.theme-toggle[data-theme='light'] {
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.16);
}

.theme-toggle[data-theme='dark'] {
    box-shadow: inset 0 0 0 1px rgba(15, 23, 42, 0.12);
}

/* ── Language Switcher ── */
.lang-switcher-wrap {
    display: flex;
    align-items: center;
}

.lang-switcher {
    background: var(--color-bg-tertiary);
    color: var(--color-text-primary);
    border: 1px solid var(--color-bg-tertiary);
    border-radius: 6px;
    padding: 5px 10px;
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: border-color 0.2s;
    outline: none;
}

.lang-switcher:hover,
.lang-switcher:focus {
    border-color: var(--color-accent);
}

.lang-switcher option {
    background: var(--color-bg-secondary);
    color: var(--color-text-primary);
}

.header-stats {
    display: flex;
    gap: 24px;
    align-items: center;
}

.header-stat {
    display: flex;
    align-items: center;
    gap: 10px;
}

.header-stat-text {
    font-size: 0.85rem;
    line-height: 1.3;
}

.progress-circle {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background: conic-gradient(var(--color-accent) 0deg, var(--color-bg-tertiary) 0deg);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    position: relative;
    flex-shrink: 0;
}

.progress-circle::before {
    content: '';
    position: absolute;
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background: var(--color-bg-secondary);
}

.progress-circle span {
    position: relative;
    z-index: 1;
    font-size: 0.75rem;
}

.stat-value-sm {
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--color-accent);
    min-width: 40px;
    text-align: center;
}

/* ══════════════════════════════════════
   APP LAYOUT — SIDEBAR + MAIN
   ══════════════════════════════════════ */
.app-layout {
    display: flex;
    flex: 1;
    overflow: hidden;
}

.site-footer {
    flex-shrink: 0;
    padding: 12px 24px;
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-bg-tertiary);
}

.site-footer-links {
    display: flex;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
    color: var(--color-text-secondary);
    font-size: 0.88rem;
}

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

.site-footer-links a:hover,
.site-footer-links a:focus {
    text-decoration: underline;
}

.noscript-banner {
    position: fixed;
    right: 20px;
    bottom: 20px;
    max-width: 360px;
    padding: 14px 16px;
    border-radius: 12px;
    background: var(--color-warning);
    color: #111827;
    box-shadow: 0 10px 26px rgba(0, 0, 0, 0.25);
    font-size: 0.9rem;
    font-weight: 600;
    z-index: 1000;
}

/* ── Sidebar ── */
.sidebar {
    width: var(--sidebar-width);
    background: var(--color-bg-secondary);
    border-right: 1px solid var(--color-bg-tertiary);
    display: flex;
    flex-direction: column;
    flex-shrink: 0;
    overflow: hidden;
}

.sidebar-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px 18px;
    border-bottom: 1px solid var(--color-bg-tertiary);
}

.sidebar-header h2 {
    font-size: 1rem;
    color: var(--color-text-primary);
}

.sidebar-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--color-text-primary);
    font-size: 1.4rem;
    cursor: pointer;
}

.mobile-toggle {
    display: none;
}

.sidebar-nav {
    overflow-y: auto;
    flex: 1;
    padding: 8px 0;
}

.sidebar-search {
    position: sticky;
    top: 0;
    z-index: 2;
    padding: 14px 18px 12px;
    background: var(--color-bg-secondary);
    border-bottom: 1px solid var(--color-bg-tertiary);
}

.sidebar-search-label {
    display: block;
    margin-bottom: 8px;
    font-size: 0.72rem;
    font-weight: 700;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--color-accent);
}

.sidebar-search-row {
    display: flex;
    align-items: center;
    gap: 8px;
}

.sidebar-search-input {
    flex: 1;
    min-width: 0;
    padding: 10px 12px;
    border: 1px solid var(--color-bg-tertiary);
    border-radius: 12px;
    background: var(--color-bg-primary);
    color: var(--color-text-primary);
    font: inherit;
    transition: border-color 0.15s, box-shadow 0.15s;
}

.sidebar-search-input::placeholder {
    color: var(--color-text-secondary);
}

.sidebar-search-input:focus {
    outline: none;
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.12);
}

.sidebar-search-clear {
    flex-shrink: 0;
    padding: 10px 12px;
    border: 1px solid var(--color-bg-tertiary);
    border-radius: 12px;
    background: var(--color-bg-primary);
    color: var(--color-text-primary);
    font: inherit;
    font-size: 0.82rem;
    cursor: pointer;
    transition: border-color 0.15s, background 0.15s, color 0.15s, opacity 0.15s;
}

.sidebar-search-clear:hover:not(:disabled),
.sidebar-search-clear:focus:not(:disabled) {
    border-color: var(--color-accent);
    color: var(--color-accent);
}

.sidebar-search-clear:disabled {
    opacity: 0.45;
    cursor: default;
}

.sidebar-search-summary {
    margin-top: 8px;
    color: var(--color-text-secondary);
    font-size: 0.78rem;
    line-height: 1.45;
}

.sidebar-search-summary.has-results {
    color: var(--color-accent);
}

.sidebar-search-summary.no-results {
    color: var(--color-warning);
}

.sidebar-search-empty {
    padding: 18px 18px 22px;
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    line-height: 1.65;
}

.sidebar-search-empty strong {
    display: block;
    margin-bottom: 6px;
    color: var(--color-text-primary);
}

.sidebar-fallback {
    padding: 16px 18px 22px;
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    line-height: 1.65;
}

.sidebar-fallback ul {
    margin: 12px 0 0 18px;
}

.sidebar-fallback li {
    margin-bottom: 8px;
}

/* Level groups */
.level-group {
    margin-bottom: 4px;
}

.level-group-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 18px;
    font-weight: 700;
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    color: var(--color-accent);
    cursor: pointer;
    user-select: none;
    transition: background 0.2s;
}

.level-group-header:hover {
    background: var(--color-bg-tertiary);
}

.level-group-header .chevron {
    transition: transform 0.2s;
    font-size: 0.7rem;
}

.level-group-header.collapsed .chevron {
    transform: rotate(-90deg);
}

.level-group-topics {
    overflow: hidden;
    transition: max-height 0.3s ease;
}

.level-group-topics.collapsed {
    max-height: 0 !important;
}

.level-group-progress {
    font-size: 0.7rem;
    color: var(--color-text-secondary);
    font-weight: 400;
    white-space: nowrap;
}

/* Topic items in sidebar */
.topic-nav-item {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 8px 18px 8px 28px;
    font-size: 0.88rem;
    color: var(--color-text-secondary);
    cursor: pointer;
    transition: all 0.15s;
    border-left: 3px solid transparent;
}

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

.topic-nav-item.active {
    background: rgba(56, 189, 248, 0.1);
    border-left-color: var(--color-accent);
    color: var(--color-accent);
    font-weight: 600;
}

.topic-nav-item .status-dot {
    width: 14px;
    height: 14px;
    border-radius: 50%;
    border: 2px solid var(--color-bg-tertiary);
    flex-shrink: 0;
}

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

.topic-nav-item .topic-name {
    flex: 1;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.topic-match-count {
    flex-shrink: 0;
    padding: 2px 7px;
    border-radius: 999px;
    border: 1px solid rgba(56, 189, 248, 0.18);
    background: rgba(56, 189, 248, 0.12);
    color: var(--color-accent);
    font-size: 0.72rem;
    font-weight: 700;
    line-height: 1;
}

mark.search-highlight {
    padding: 0 0.14em;
    border-radius: 0.25em;
    background: rgba(245, 158, 11, 0.28);
    color: inherit;
    box-decoration-break: clone;
    -webkit-box-decoration-break: clone;
}

/* ── Main Content ── */
.main-content {
    flex: 1;
    overflow-y: auto;
    padding: 32px 40px;
}

/* ══════════════════════════════════════
   WELCOME VIEW
   ══════════════════════════════════════ */
.welcome-view h2 {
    font-size: 1.6rem;
    color: var(--color-accent);
    margin-bottom: 8px;
}

.welcome-view p {
    color: var(--color-text-secondary);
    margin-bottom: 24px;
    max-width: 700px;
}

.welcome-view-static {
    max-width: 900px;
}

.static-summary {
    background: var(--color-bg-secondary);
    padding: 20px 24px;
    border-radius: 12px;
    border-left: 4px solid var(--color-accent);
}

.static-summary h3 {
    color: var(--color-accent);
    margin-bottom: 10px;
    font-size: 1.05rem;
}

.static-summary ul {
    margin-left: 18px;
    color: var(--color-text-secondary);
}

.static-summary li {
    margin-bottom: 6px;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: 16px;
    margin-bottom: 32px;
}

.stat-card {
    background: var(--color-bg-secondary);
    padding: 20px;
    border-radius: 12px;
    text-align: center;
}

.stat-value {
    font-size: 2.2rem;
    font-weight: bold;
    color: var(--color-accent);
}

.stat-label {
    color: var(--color-text-secondary);
    margin-top: 4px;
    font-size: 0.9rem;
}

.achievements-section h3 {
    margin-bottom: 16px;
    color: var(--color-text-primary);
}

.achievements-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 12px;
}

.achievement {
    background: var(--color-bg-secondary);
    padding: 16px;
    border-radius: 12px;
    text-align: center;
    transition: all 0.3s;
}

.achievement.unlocked {
    border: 2px solid var(--color-success);
}

.achievement.locked {
    opacity: 0.5;
}

.achievement-icon { font-size: 2.5rem; margin-bottom: 6px; }
.achievement-title { font-weight: 600; font-size: 0.88rem; margin-bottom: 4px; }
.achievement-desc { font-size: 0.78rem; color: var(--color-text-secondary); }

/* ══════════════════════════════════════
   TOPIC VIEW
   ══════════════════════════════════════ */
.topic-view {
    max-width: 900px;
}

.topic-header {
    margin-bottom: 24px;
}

.topic-header .badge {
    margin-bottom: 8px;
}

.topic-header h2 {
    font-size: 1.5rem;
    color: var(--color-accent);
    margin-bottom: 4px;
}

.topic-header .topic-level-label {
    font-size: 0.85rem;
    color: var(--color-text-secondary);
}

.topic-lesson {
    color: var(--color-text-secondary);
    line-height: 1.8;
    margin-bottom: 28px;
}

.topic-lesson h3 {
    color: var(--color-accent);
    margin: 20px 0 10px;
}

.topic-lesson ul, .topic-lesson ol {
    margin-left: 20px;
    margin-bottom: 10px;
}

.topic-lesson li {
    margin-bottom: 4px;
}

.topic-lesson table {
    width: 100%;
    border-collapse: collapse;
    margin: 12px 0;
}

.topic-lesson th, .topic-lesson td {
    border: 1px solid var(--color-bg-tertiary);
    padding: 8px 12px;
    text-align: left;
}

.topic-lesson th {
    background: var(--color-bg-tertiary);
}

.key-points {
    background: var(--color-bg-secondary);
    padding: 20px 24px;
    border-radius: 12px;
    margin-bottom: 32px;
    border-left: 4px solid var(--color-accent);
}

.key-points h3 {
    color: var(--color-accent);
    margin-bottom: 10px;
    font-size: 1.05rem;
}

.key-points ul {
    margin-left: 18px;
}

.key-points li {
    margin-bottom: 4px;
}

/* ══════════════════════════════════════
   VISUAL REFERENCE LINKS
   ══════════════════════════════════════ */
.visual-ref-links {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin: 16px 0 24px;
}

.visual-ref-btn {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 10px 18px;
    background: linear-gradient(135deg, var(--color-bg-tertiary), var(--color-bg-secondary));
    border: 1px solid var(--color-accent);
    border-radius: 10px;
    color: var(--color-accent);
    font-size: 0.88rem;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: all 0.25s ease;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
}

.visual-ref-btn:hover {
    background: var(--color-accent);
    color: var(--color-bg-primary);
    transform: translateY(-2px);
    box-shadow: 0 4px 16px rgba(99, 102, 241, 0.35);
}

/* ── Visual Reference Modal ── */
.visual-ref-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: var(--color-overlay);
    backdrop-filter: blur(4px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 10000;
    opacity: 0;
    transition: opacity 0.2s ease;
}

.visual-ref-overlay.active {
    opacity: 1;
}

.visual-ref-modal {
    width: 90vw;
    height: 85vh;
    max-width: 1200px;
    background: var(--color-bg-primary);
    border: 1px solid var(--color-border);
    border-radius: 16px;
    overflow: hidden;
    display: flex;
    flex-direction: column;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
}

.visual-ref-modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 20px;
    background: var(--color-bg-secondary);
    border-bottom: 1px solid var(--color-border);
    font-weight: 600;
    font-size: 0.95rem;
}

.visual-ref-close {
    background: none;
    border: none;
    color: var(--color-text-secondary);
    font-size: 1.2rem;
    cursor: pointer;
    padding: 4px 8px;
    border-radius: 6px;
    transition: all 0.15s;
}

.visual-ref-close:hover {
    background: var(--color-bg-tertiary);
    color: var(--color-text-primary);
}

.visual-ref-iframe {
    flex: 1;
    width: 100%;
    border: none;
    background: #fff;
}

.visual-ref-modal-footer {
    padding: 8px 20px;
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border);
    text-align: right;
}

.visual-ref-open-tab {
    color: var(--color-accent);
    text-decoration: none;
    font-size: 0.85rem;
    font-weight: 500;
}

.visual-ref-open-tab:hover {
    text-decoration: underline;
}

/* ══════════════════════════════════════
   RELATED TOPICS & RESOURCES
   ══════════════════════════════════════ */
.related-topics {
    margin-bottom: 24px;
}

.related-topics h3, .external-resources h3 {
    font-size: 1rem;
    margin-bottom: 10px;
    color: var(--color-text-secondary);
}

.related-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.related-chip {
    display: inline-block;
    padding: 6px 14px;
    background: var(--color-bg-tertiary);
    border: 1px solid var(--color-accent);
    border-radius: 20px;
    color: var(--color-accent);
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
}

.related-chip:hover {
    background: var(--color-accent);
    color: var(--color-bg-primary);
    transform: translateY(-1px);
}

.external-resources {
    margin-bottom: 24px;
}

.external-resources ul {
    margin-left: 18px;
}

.external-resources a {
    color: var(--color-accent);
    text-decoration: none;
    font-weight: 500;
    transition: opacity 0.2s;
}

.external-resources a:hover {
    opacity: 0.8;
    text-decoration: underline;
}

/* ══════════════════════════════════════
   EXERCISES SECTION (inline in topic)
   ══════════════════════════════════════ */
.exercises-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 16px;
}

.exercises-header h3 {
    margin-bottom: 0;
}

.btn-small {
    padding: 6px 14px;
    font-size: 0.82rem;
}

.exercises-section {
    margin-bottom: 32px;
}

.exercises-section h3, .scenarios-section h3 {
    font-size: 1.15rem;
    margin-bottom: 16px;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--color-bg-tertiary);
}

.quiz-card {
    background: var(--color-bg-secondary);
    padding: 24px;
    border-radius: 12px;
    margin-bottom: 16px;
}

.quiz-card .question-text {
    font-size: 1.05rem;
    font-weight: 600;
    margin-bottom: 14px;
    color: var(--color-text-primary);
}

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

.option {
    padding: 12px 16px;
    background: var(--color-bg-tertiary);
    border: 2px solid transparent;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 0.95rem;
}

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

.option.selected {
    border-color: var(--color-accent);
    background: var(--color-accent);
    color: var(--color-bg-primary);
}

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

.option.incorrect {
    border-color: var(--color-danger);
    background: var(--color-danger);
    color: white;
}

.quiz-actions {
    display: flex;
    gap: 12px;
    margin-top: 14px;
}

/* Calculation exercise type */
.question-badge {
    display: inline-block;
    background: var(--color-accent);
    color: var(--color-bg-primary);
    padding: 3px 10px;
    border-radius: 12px;
    font-size: 0.78rem;
    font-weight: 700;
    margin-bottom: 10px;
    letter-spacing: 0.5px;
}

.calc-input-group {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-top: 8px;
}

.calc-input {
    width: 200px;
    padding: 10px 14px;
    background: var(--color-bg-tertiary);
    border: 2px solid var(--color-bg-tertiary);
    border-radius: 8px;
    color: var(--color-text-primary);
    font-size: 1rem;
    font-family: 'Inter', sans-serif;
    transition: border-color 0.2s;
}

.calc-input:focus {
    outline: none;
    border-color: var(--color-accent);
}

.calc-unit {
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    font-weight: 600;
}

/* True/False option styling */
.tf-options {
    flex-direction: row !important;
    gap: 12px !important;
}

.tf-option {
    flex: 1;
    text-align: center;
    font-weight: 600;
    font-size: 1rem !important;
    padding: 16px !important;
}

.result-message {
    padding: 14px 18px;
    border-radius: 8px;
    margin-top: 14px;
    font-size: 0.92rem;
    line-height: 1.5;
}

.result-success {
    background: rgba(34, 197, 94, 0.15);
    border: 1px solid var(--color-success);
    color: var(--color-success);
}

.result-error {
    background: rgba(239, 68, 68, 0.15);
    border: 1px solid var(--color-danger);
    color: var(--color-danger);
}

/* ══════════════════════════════════════
   SCENARIO SECTION (inline in topic)
   ══════════════════════════════════════ */
.scenario-card {
    background: var(--color-bg-secondary);
    padding: 24px;
    border-radius: 12px;
    margin-bottom: 16px;
}

.scenario-card h4 {
    font-size: 1.05rem;
    color: var(--color-text-primary);
    margin-bottom: 8px;
}

.scenario-card .scenario-desc {
    color: var(--color-text-secondary);
    margin-bottom: 14px;
    font-size: 0.95rem;
}

.scenario-choices {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.choice-card {
    padding: 12px 16px;
    background: var(--color-bg-tertiary);
    border: 2px solid transparent;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 0.95rem;
}

.choice-card:hover { border-color: var(--color-accent); }

/* ══════════════════════════════════════
   COMPLETE BUTTON
   ══════════════════════════════════════ */
.topic-actions {
    display: flex;
    gap: 12px;
    margin-top: 32px;
    padding-top: 24px;
    border-top: 2px solid var(--color-bg-tertiary);
}

.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s;
    font-weight: 600;
}

.btn-primary {
    background: var(--color-accent);
    color: var(--color-bg-primary);
}

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

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

.btn-secondary:hover { background: var(--color-bg-secondary); }

.btn-success {
    background: var(--color-success);
    color: white;
    cursor: default;
}

.badge {
    display: inline-block;
    padding: 3px 10px;
    border-radius: 10px;
    font-size: 0.75rem;
    font-weight: 600;
}

.badge-robotics { background: var(--color-robotics); color: white; }
.badge-embedded { background: var(--color-embedded); color: white; }
.badge-essential { background: var(--color-essential); color: white; }

/* ══════════════════════════════════════
   RESPONSIVE
   ══════════════════════════════════════ */
@media (max-width: 900px) {
    .app-header {
        flex-wrap: wrap;
        align-items: flex-start;
    }

    .header-left {
        gap: 10px;
        width: 100%;
    }

    .app-logo {
        width: 48px;
        height: 48px;
        border-radius: 12px;
    }

    .header-controls {
        gap: 10px;
    }

    .sidebar {
        position: fixed;
        left: 0;
        top: 0;
        bottom: 0;
        z-index: 100;
        transform: translateX(-100%);
        transition: transform 0.3s;
        box-shadow: 4px 0 20px rgba(0,0,0,0.3);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .sidebar-toggle {
        display: block;
    }

    .app-header h1 {
        font-size: 1rem;
    }

    .repo-link {
        padding: 5px 10px;
        font-size: 0.76rem;
    }

    .theme-toggle {
        width: 36px;
        height: 36px;
        font-size: 0.95rem;
    }

    .header-stats {
        gap: 12px;
        width: 100%;
        justify-content: flex-start;
    }

    .main-content {
        padding: 20px;
    }

    .site-footer {
        padding: 12px 20px;
    }

    .mobile-toggle {
        display: block;
        position: fixed;
        bottom: 24px;
        left: 24px;
        z-index: 99;
        width: 48px;
        height: 48px;
        border-radius: 50%;
        background: var(--color-accent);
        color: var(--color-bg-primary);
        border: none;
        font-size: 1.5rem;
        cursor: pointer;
        box-shadow: 0 4px 12px rgba(0,0,0,0.3);
    }
}

/* Scrollbar styling */
.sidebar-nav::-webkit-scrollbar,
.main-content::-webkit-scrollbar {
    width: 6px;
}

.sidebar-nav::-webkit-scrollbar-track,
.main-content::-webkit-scrollbar-track {
    background: transparent;
}

.sidebar-nav::-webkit-scrollbar-thumb,
.main-content::-webkit-scrollbar-thumb {
    background: var(--color-bg-tertiary);
    border-radius: 3px;
}

/* Animations */
@keyframes slideIn {
    from { transform: translateX(100px); opacity: 0; }
    to { transform: translateX(0); opacity: 1; }
}

@keyframes slideOut {
    from { transform: translateX(0); opacity: 1; }
    to { transform: translateX(100px); opacity: 0; }
}