/* ============================================================
   CheesCoach Course — Styles
   Extends the shared design system (variables, components, utilities)
   Used by both the course hub and individual lesson pages
   ============================================================ */

/* ============================================================
   HUB — Hero Section
   ============================================================ */
.course-hero {
    padding: calc(var(--space-24) + var(--space-8)) var(--space-6) var(--space-12);
    text-align: center;
    position: relative;
    overflow: hidden;
    background:
        radial-gradient(ellipse 80% 50% at 50% -5%, rgba(79, 143, 247, 0.10) 0%, transparent 60%),
        radial-gradient(ellipse 40% 30% at 80% 20%, rgba(212, 168, 67, 0.05) 0%, transparent 50%),
        var(--bg-primary);
}

.course-hero-inner {
    max-width: 720px;
    margin: 0 auto;
    position: relative;
    z-index: 1;
}

.course-hero-title {
    font-family: var(--font-display);
    font-size: var(--text-5xl);
    font-weight: 800;
    line-height: var(--leading-tight);
    margin-bottom: var(--space-4);
    animation: fadeInUp 0.6s ease both;
}

.course-hero-title .highlight {
    background: linear-gradient(135deg, var(--accent-bright), var(--gold));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.course-hero-subtitle {
    font-size: var(--text-lg);
    color: var(--text-secondary);
    line-height: var(--leading-normal);
    max-width: 560px;
    margin: 0 auto var(--space-10);
    animation: fadeInUp 0.6s ease 0.1s both;
}

/* --- Course Progress Bar (Hub) --- */
.course-progress {
    max-width: 480px;
    margin: 0 auto;
    animation: fadeInUp 0.6s ease 0.2s both;
}

.course-progress-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--space-2);
}

.course-progress-label {
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--text-secondary);
}

.course-progress-count {
    font-size: var(--text-sm);
    font-weight: 700;
    color: var(--accent-bright);
    font-family: var(--font-display);
}

.course-progress-track {
    width: 100%;
    height: 10px;
    background: var(--bg-secondary);
    border-radius: var(--radius-full);
    overflow: hidden;
    border: 1px solid var(--border-subtle);
}

.course-progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-dim), var(--accent), var(--accent-bright));
    border-radius: var(--radius-full);
    transition: width 0.8s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    min-width: 0;
}

.course-progress-fill::after {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    animation: shimmer 2s infinite;
}

/* ============================================================
   HUB — Lessons Grid
   ============================================================ */
.lessons-section {
    padding: var(--space-8) var(--space-6) var(--space-16);
}

.lessons-section .container {
    max-width: var(--container-xl);
}

/* --- Lesson Card --- */
.lesson-card {
    position: relative;
    display: flex;
    flex-direction: column;
    background: var(--bg-glass);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: var(--space-8) var(--space-6) var(--space-6);
    cursor: pointer;
    transition: all var(--transition);
    text-decoration: none;
    color: inherit;
    overflow: hidden;
    animation: fadeInUp 0.5s ease both;
}

.lesson-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--border);
    transition: background var(--transition);
}

.lesson-card::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 1px;
    background: linear-gradient(90deg, transparent, rgba(79, 143, 247, 0.3), transparent);
    opacity: 0;
    transition: opacity var(--transition);
}

.lesson-card:hover {
    transform: translateY(-6px);
    border-color: var(--border-hover);
    background: var(--bg-glass-hover);
    box-shadow: var(--shadow-glow-blue), var(--shadow-md);
    text-decoration: none;
    color: inherit;
}

.lesson-card:hover::after {
    opacity: 1;
}

.lesson-card:hover .lesson-card-icon {
    transform: scale(1.15);
}

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

/* --- Card States --- */
.lesson-card.completed::before {
    background: linear-gradient(90deg, var(--success-dim), var(--success));
}

.lesson-card.completed {
    border-color: rgba(52, 211, 153, 0.2);
}

.lesson-card.completed:hover {
    border-color: rgba(52, 211, 153, 0.4);
    box-shadow: 0 0 40px rgba(52, 211, 153, 0.1), var(--shadow-md);
}

.lesson-card.current::before {
    background: linear-gradient(90deg, var(--accent-dim), var(--accent-bright));
}

.lesson-card.current {
    border-color: rgba(79, 143, 247, 0.3);
    box-shadow: 0 0 30px rgba(79, 143, 247, 0.08);
    animation: fadeInUp 0.5s ease both, glow 3s ease-in-out infinite;
}

.lesson-card.current:hover {
    border-color: rgba(79, 143, 247, 0.5);
    box-shadow: 0 0 40px rgba(79, 143, 247, 0.15), var(--shadow-md);
}

.lesson-card.locked {
    opacity: 0.45;
    pointer-events: none;
    cursor: default;
}

.lesson-card.locked::before {
    background: var(--border-subtle);
}

/* --- Lesson Number Badge --- */
.lesson-card-number {
    position: absolute;
    top: var(--space-3);
    left: var(--space-3);
    width: 30px;
    height: 30px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    color: var(--text-muted);
    font-family: var(--font-display);
    font-size: var(--text-xs);
    font-weight: 700;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

.lesson-card.completed .lesson-card-number {
    background: var(--success);
    border-color: var(--success);
    color: white;
}

.lesson-card.current .lesson-card-number {
    background: var(--accent);
    border-color: var(--accent);
    color: white;
    box-shadow: 0 0 12px rgba(79, 143, 247, 0.4);
}

/* --- Status Badge --- */
.lesson-card-status {
    position: absolute;
    top: var(--space-3);
    right: var(--space-3);
    font-size: 0.65rem;
    font-weight: 700;
    padding: 2px var(--space-3);
    border-radius: var(--radius-full);
    letter-spacing: 0.04em;
    text-transform: uppercase;
}

.lesson-card-status.status-completed {
    background: rgba(52, 211, 153, 0.1);
    border: 1px solid rgba(52, 211, 153, 0.3);
    color: var(--success);
}

.lesson-card-status.status-current {
    background: var(--accent-glow);
    border: 1px solid rgba(79, 143, 247, 0.3);
    color: var(--accent-bright);
    animation: pulse 2s ease-in-out infinite;
}

.lesson-card-status.status-locked {
    background: rgba(90, 109, 138, 0.1);
    border: 1px solid rgba(90, 109, 138, 0.2);
    color: var(--text-muted);
    font-size: var(--text-sm);
}

/* --- Card Icon --- */
.lesson-card-icon {
    font-size: 3rem;
    margin: var(--space-3) 0 var(--space-4);
    text-align: center;
    line-height: 1;
    transition: transform var(--transition);
    filter: drop-shadow(0 4px 12px rgba(0, 0, 0, 0.3));
}

/* --- Card Content --- */
.lesson-card-title {
    font-family: var(--font-display);
    font-size: var(--text-lg);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--space-2);
    line-height: var(--leading-snug);
}

.lesson-card-description {
    font-size: var(--text-sm);
    color: var(--text-secondary);
    line-height: var(--leading-relaxed);
    flex: 1;
}

/* --- Card Footer --- */
.lesson-card-footer {
    display: flex;
    align-items: center;
    justify-content: flex-end;
    margin-top: var(--space-4);
    padding-top: var(--space-3);
    border-top: 1px solid var(--border-subtle);
}

.lesson-card-arrow {
    display: flex;
    align-items: center;
    gap: var(--space-1);
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--accent-bright);
    opacity: 0;
    transform: translateX(-8px);
    transition: all var(--transition);
}

.lesson-card.current .lesson-card-arrow {
    opacity: 1;
    transform: translateX(0);
}

.lesson-card-arrow svg {
    width: 16px;
    height: 16px;
}

/* --- Stagger animation delays for grid cards --- */
.lesson-card:nth-child(1)  { animation-delay: 0.05s; }
.lesson-card:nth-child(2)  { animation-delay: 0.10s; }
.lesson-card:nth-child(3)  { animation-delay: 0.15s; }
.lesson-card:nth-child(4)  { animation-delay: 0.20s; }
.lesson-card:nth-child(5)  { animation-delay: 0.25s; }
.lesson-card:nth-child(6)  { animation-delay: 0.30s; }
.lesson-card:nth-child(7)  { animation-delay: 0.35s; }
.lesson-card:nth-child(8)  { animation-delay: 0.40s; }
.lesson-card:nth-child(9)  { animation-delay: 0.45s; }
.lesson-card:nth-child(10) { animation-delay: 0.50s; }

/* ============================================================
   HUB — CTA Section
   ============================================================ */
.course-cta {
    padding: var(--space-4) var(--space-6) var(--space-16);
}

.course-cta-card {
    max-width: 800px;
    margin: 0 auto;
    background:
        linear-gradient(135deg, var(--accent-glow), var(--gold-glow));
    border: 1px solid var(--border);
    border-radius: var(--radius-xl);
    padding: var(--space-12) var(--space-8);
    text-align: center;
    position: relative;
    overflow: hidden;
}

.course-cta-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--accent), var(--gold), var(--accent-bright));
}

.course-cta-icon {
    font-size: var(--text-5xl);
    margin-bottom: var(--space-4);
    display: block;
}

.course-cta-title {
    font-family: var(--font-display);
    font-size: var(--text-2xl);
    font-weight: 800;
    color: var(--text-primary);
    margin-bottom: var(--space-3);
}

.course-cta-text {
    font-size: var(--text-base);
    color: var(--text-secondary);
    line-height: var(--leading-normal);
    margin-bottom: var(--space-6);
    max-width: 480px;
    margin-left: auto;
    margin-right: auto;
}

/* ============================================================
   LESSON PAGES — Layout
   ============================================================ */
.lesson-layout {
    display: flex;
    min-height: 100vh;
}

/* --- Sidebar --- */
.course-sidebar {
    position: fixed;
    left: 0;
    top: 64px;
    bottom: 0;
    width: 260px;
    background: var(--bg-glass);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    z-index: var(--z-dropdown);
    overflow: hidden;
    transition: transform var(--transition);
}

.sidebar-header {
    padding: var(--space-5) var(--space-4);
    border-bottom: 1px solid var(--border-subtle);
    flex-shrink: 0;
}

.sidebar-header h2 {
    font-family: var(--font-display);
    font-size: var(--text-base);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--space-1);
}

.sidebar-header p {
    font-size: var(--text-xs);
    color: var(--text-muted);
}

.sidebar-nav {
    flex: 1;
    overflow-y: auto;
    padding: var(--space-3) 0;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
}

.sidebar-nav::-webkit-scrollbar {
    width: 4px;
}

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

.sidebar-nav::-webkit-scrollbar-thumb {
    background-color: var(--border);
    border-radius: 2px;
}

.sidebar-nav ul {
    list-style: none;
}

.sidebar-lesson-link {
    display: flex;
    align-items: center;
    gap: var(--space-3);
    padding: var(--space-3) var(--space-4);
    color: var(--text-secondary);
    text-decoration: none;
    font-size: var(--text-sm);
    transition: all var(--transition-fast);
    border-left: 3px solid transparent;
    cursor: pointer;
}

.sidebar-lesson-link:hover {
    background: var(--bg-glass-hover);
    color: var(--text-primary);
    text-decoration: none;
}

.sidebar-lesson-link.completed {
    color: var(--success);
}

.sidebar-lesson-link.completed .sidebar-lesson-number {
    background: var(--success);
    color: white;
    border-color: var(--success);
}

.sidebar-lesson-link.current {
    background: var(--accent-glow);
    color: var(--accent-bright);
    border-left-color: var(--accent);
    font-weight: 500;
}

.sidebar-lesson-link.current .sidebar-lesson-number {
    background: var(--accent);
    color: white;
    border-color: var(--accent);
}

.sidebar-lesson-link.locked {
    color: var(--text-muted);
    cursor: default;
    opacity: 0.5;
}

.sidebar-lesson-link.locked:hover {
    background: transparent;
    color: var(--text-muted);
}

.sidebar-lesson-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    font-size: var(--text-xs);
    font-weight: 600;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

.sidebar-lesson-title {
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

/* --- Sidebar Overlay (mobile) --- */
.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: calc(var(--z-dropdown) - 1);
    opacity: 0;
    transition: opacity var(--transition);
}

.sidebar-overlay.visible {
    opacity: 1;
}

/* --- Main Content Area --- */
.lesson-main {
    flex: 1;
    margin-left: 260px;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* --- Lesson Header Bar --- */
.lesson-header {
    position: sticky;
    top: 64px;
    z-index: calc(var(--z-dropdown) - 10);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 var(--space-6);
    height: 56px;
    background: var(--bg-glass);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-subtle);
}

.header-back {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    color: var(--text-secondary);
    font-size: var(--text-sm);
    font-weight: 500;
    text-decoration: none;
    transition: color var(--transition-fast);
}

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

.header-info {
    font-size: var(--text-xs);
    color: var(--text-muted);
    font-weight: 500;
}

.header-info strong {
    color: var(--accent-bright);
    font-weight: 600;
}

/* Hamburger (mobile) */
.hamburger-btn {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: var(--text-2xl);
    cursor: pointer;
    padding: var(--space-1);
    line-height: 1;
}

/* --- Lesson Progress Bar (inline) --- */
.lesson-progress {
    position: relative;
    height: 4px;
    background: var(--bg-secondary);
    flex-shrink: 0;
}

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

.lesson-progress-text {
    position: absolute;
    right: var(--space-4);
    top: 8px;
    font-size: 0.7rem;
    color: var(--text-muted);
    font-weight: 500;
}

/* ============================================================
   LESSON PAGES — Content
   ============================================================ */
.lesson-content {
    flex: 1;
    max-width: 900px;
    width: 100%;
    margin: 0 auto;
    padding: var(--space-8) var(--space-8) var(--space-16);
}

/* --- Title Section --- */
.lesson-title-section {
    margin-bottom: var(--space-10);
    padding-bottom: var(--space-6);
    border-bottom: 1px solid var(--border-subtle);
    animation: fadeIn 0.5s ease;
}

.lesson-title {
    font-family: var(--font-display);
    font-size: var(--text-4xl);
    font-weight: 800;
    color: var(--text-primary);
    line-height: var(--leading-tight);
    margin-bottom: var(--space-2);
}

.lesson-description {
    font-size: var(--text-lg);
    color: var(--text-secondary);
    line-height: var(--leading-normal);
}

/* --- Text Blocks --- */
.lesson-text {
    font-size: var(--text-base);
    line-height: var(--leading-relaxed);
    color: var(--text-secondary);
    margin-bottom: var(--space-6);
}

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

.lesson-text em {
    color: var(--accent-bright);
    font-style: italic;
}

.lesson-text code {
    background: var(--bg-secondary);
    padding: 2px var(--space-2);
    border-radius: var(--radius-sm);
    font-size: 0.9em;
    color: var(--accent-bright);
    font-family: var(--font-mono);
}

.lesson-subtitle {
    font-family: var(--font-display);
    font-size: var(--text-2xl);
    font-weight: 700;
    color: var(--text-primary);
    margin-top: var(--space-10);
    margin-bottom: var(--space-4);
    line-height: var(--leading-snug);
}

.lesson-small-heading {
    font-family: var(--font-display);
    font-size: var(--text-xl);
    font-weight: 600;
    color: var(--text-primary);
    margin-top: var(--space-6);
    margin-bottom: var(--space-3);
}

/* --- Concept Box --- */
.concept-box {
    background: var(--accent-glow);
    border: 1px solid rgba(79, 143, 247, 0.15);
    border-left: 4px solid var(--accent);
    border-radius: var(--radius-md);
    padding: var(--space-5) var(--space-6);
    margin-bottom: var(--space-6);
}

.concept-box-title {
    font-family: var(--font-display);
    font-size: var(--text-sm);
    font-weight: 700;
    color: var(--accent-bright);
    margin-bottom: var(--space-2);
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.concept-box-title::before {
    content: "\1F4A1";
    font-size: var(--text-base);
}

.concept-box p {
    font-size: var(--text-sm);
    line-height: var(--leading-normal);
    color: var(--text-secondary);
}

.concept-box p strong {
    color: var(--text-primary);
}

/* --- Tip Box --- */
.tip-box {
    background: rgba(52, 211, 153, 0.08);
    border: 1px solid rgba(52, 211, 153, 0.2);
    border-left: 4px solid var(--success);
    border-radius: var(--radius-md);
    padding: var(--space-5) var(--space-6);
    margin-bottom: var(--space-6);
}

.tip-box-title {
    font-family: var(--font-display);
    font-size: var(--text-sm);
    font-weight: 700;
    color: var(--success);
    margin-bottom: var(--space-2);
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.tip-box-title::before {
    content: "\2705";
    font-size: var(--text-base);
}

.tip-box p {
    font-size: var(--text-sm);
    line-height: var(--leading-normal);
    color: var(--text-secondary);
}

/* --- Warning Box --- */
.warning-box {
    background: rgba(251, 191, 36, 0.08);
    border: 1px solid rgba(251, 191, 36, 0.2);
    border-left: 4px solid var(--warning);
    border-radius: var(--radius-md);
    padding: var(--space-5) var(--space-6);
    margin-bottom: var(--space-6);
}

.warning-box-title {
    font-family: var(--font-display);
    font-size: var(--text-sm);
    font-weight: 700;
    color: var(--warning);
    margin-bottom: var(--space-2);
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.warning-box-title::before {
    content: "\26A0\FE0F";
    font-size: var(--text-base);
}

.warning-box p {
    font-size: var(--text-sm);
    line-height: var(--leading-normal);
    color: var(--text-secondary);
}

/* --- Piece Values Grid --- */
.piece-values {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: var(--space-3);
    margin-bottom: var(--space-6);
}

.piece-value-item {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-4);
    background: var(--bg-glass);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    font-size: var(--text-sm);
}

.piece-value-item .piece-icon {
    font-size: var(--text-xl);
}

.piece-value-item .piece-name {
    color: var(--text-secondary);
}

.piece-value-item .piece-pts {
    margin-left: auto;
    color: var(--accent-bright);
    font-weight: 600;
    font-family: var(--font-display);
}

/* ============================================================
   LESSON PAGES — Chess Board
   ============================================================ */
.board-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    margin: var(--space-6) auto;
    width: min(360px, 80vw, 48vh);
}

.board-container chess-board {
    width: 100%;
    max-width: 100%;
    --light-color: var(--board-light);
    --dark-color: var(--board-dark);
    --highlight-color: var(--board-highlight);
    border-radius: var(--radius-sm);
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

.board-caption {
    margin-top: var(--space-3);
    font-size: var(--text-sm);
    color: var(--text-muted);
    text-align: center;
    font-style: italic;
    line-height: var(--leading-normal);
}

/* Board with instruction panel (side by side on desktop) */
.board-with-panel {
    display: flex;
    gap: var(--space-6);
    align-items: flex-start;
    margin: var(--space-6) 0;
}

.board-with-panel .board-side {
    flex: 0 0 min(360px, 80vw, 48vh);
}

.board-with-panel .board-side chess-board {
    width: 100%;
    --light-color: var(--board-light);
    --dark-color: var(--board-dark);
    --highlight-color: var(--board-highlight);
    border-radius: var(--radius-sm);
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

.board-with-panel .panel-side {
    flex: 1;
    min-width: 0;
}

/* ============================================================
   LESSON PAGES — Exercise Components
   ============================================================ */
.exercise-card {
    position: relative;
    background: var(--bg-glass);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: var(--space-6);
    margin-bottom: var(--space-8);
    transition: border-color var(--transition), box-shadow var(--transition);
}

.exercise-card.active {
    border-color: var(--accent);
    box-shadow: 0 0 20px var(--accent-glow);
}

.exercise-card.completed-exercise {
    border-color: var(--success);
    opacity: 0.85;
}

.exercise-badge {
    position: absolute;
    top: -10px;
    left: var(--space-5);
    background: linear-gradient(135deg, var(--accent), var(--accent-dim));
    color: white;
    font-family: var(--font-display);
    font-size: var(--text-xs);
    font-weight: 700;
    padding: 2px var(--space-3);
    border-radius: var(--radius-full);
    letter-spacing: 0.04em;
    text-transform: uppercase;
}

.exercise-badge.completed-badge {
    background: linear-gradient(135deg, var(--success), var(--success-dim));
}

.exercise-title {
    font-family: var(--font-display);
    font-size: var(--text-lg);
    font-weight: 700;
    color: var(--text-primary);
    margin-top: var(--space-1);
    margin-bottom: var(--space-3);
}

.exercise-instruction {
    font-size: var(--text-base);
    color: var(--accent-bright);
    font-weight: 500;
    line-height: var(--leading-normal);
    margin-bottom: var(--space-5);
    padding: var(--space-3) var(--space-4);
    background: var(--accent-glow);
    border-radius: var(--radius-md);
    border: 1px solid rgba(79, 143, 247, 0.12);
}

.exercise-board-area {
    display: flex;
    flex-direction: column;
    align-items: center;
    margin-bottom: var(--space-4);
    width: min(360px, 80vw, 48vh);
    margin-left: auto;
    margin-right: auto;
}

.exercise-board-area chess-board {
    width: 100% !important;
    max-width: 100%;
    --light-color: var(--board-light);
    --dark-color: var(--board-dark);
    --highlight-color: var(--board-highlight);
    border-radius: var(--radius-sm);
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

/* --- Exercise Feedback --- */
.exercise-feedback {
    padding: var(--space-3) var(--space-4);
    border-radius: var(--radius-md);
    font-size: var(--text-sm);
    line-height: var(--leading-normal);
    margin-top: var(--space-4);
    display: none;
    align-items: center;
    gap: var(--space-2);
    transition: all var(--transition);
}

.exercise-feedback.visible {
    display: flex;
}

.exercise-feedback .feedback-icon {
    font-size: var(--text-lg);
    flex-shrink: 0;
}

.feedback-correct {
    background: rgba(52, 211, 153, 0.08);
    border: 1px solid rgba(52, 211, 153, 0.25);
    color: var(--success);
}

.exercise-correct {
    box-shadow: 0 0 30px var(--board-correct);
}

.feedback-correct .feedback-icon::before {
    content: "\2705";
}

.feedback-incorrect {
    background: rgba(248, 113, 113, 0.08);
    border: 1px solid rgba(248, 113, 113, 0.25);
    color: var(--error);
}

.exercise-incorrect {
    animation: shake 0.3s;
}

.feedback-incorrect .feedback-icon::before {
    content: "\274C";
}

.feedback-hint {
    background: var(--gold-glow);
    border: 1px solid rgba(212, 168, 67, 0.25);
    color: var(--gold-bright);
}

.feedback-hint .feedback-icon::before {
    content: "\1F4A1";
}

.feedback-info {
    background: rgba(139, 157, 195, 0.08);
    border: 1px solid rgba(139, 157, 195, 0.15);
    color: var(--text-secondary);
}

.feedback-info .feedback-icon::before {
    content: "\2139\FE0F";
}

/* --- Exercise Buttons --- */
.exercise-buttons {
    display: flex;
    gap: var(--space-3);
    margin-top: var(--space-4);
    flex-wrap: wrap;
}

.exercise-btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-5);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-family: var(--font-body);
    font-size: var(--text-sm);
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.exercise-btn:hover {
    background: var(--bg-card-hover);
    color: var(--text-primary);
    border-color: var(--border-hover);
}

.exercise-btn-primary {
    background: linear-gradient(135deg, var(--accent), var(--accent-dim));
    border-color: var(--accent);
    color: white;
}

.exercise-btn-primary:hover {
    background: linear-gradient(135deg, var(--accent-bright), var(--accent));
    border-color: var(--accent-bright);
}

.exercise-btn-success {
    background: linear-gradient(135deg, var(--success), var(--success-dim));
    border-color: var(--success);
    color: white;
}

.exercise-btn-success:hover {
    background: var(--success);
    border-color: var(--success);
}

.exercise-btn:disabled {
    opacity: 0.35;
    cursor: not-allowed;
}

/* --- Sequence Step Info --- */
.sequence-step-info {
    padding: var(--space-3) var(--space-4);
    background: rgba(139, 157, 195, 0.06);
    border-radius: var(--radius-md);
    border: 1px solid var(--border-subtle);
    margin-top: var(--space-3);
    font-size: var(--text-sm);
    color: var(--text-secondary);
    line-height: var(--leading-normal);
}

.sequence-step-info strong {
    color: var(--text-primary);
}

.sequence-move-counter {
    font-size: var(--text-xs);
    color: var(--text-muted);
    margin-top: var(--space-1);
}

/* --- Exercise Explanation --- */
.exercise-explanation {
    margin-top: var(--space-4);
    padding: var(--space-4) var(--space-5);
    background: rgba(139, 157, 195, 0.05);
    border-radius: var(--radius-md);
    border-left: 3px solid var(--accent);
    font-size: var(--text-sm);
    color: var(--text-secondary);
    line-height: var(--leading-relaxed);
    display: none;
}

.exercise-explanation.visible {
    display: block;
    animation: fadeIn 0.4s ease;
}

/* ============================================================
   LESSON PAGES — Navigation Footer
   ============================================================ */
.lesson-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-6) 0;
    margin-top: var(--space-12);
    border-top: 1px solid var(--border-subtle);
}

.lesson-nav-btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-2);
    padding: var(--space-3) var(--space-6);
    background: var(--bg-glass);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    color: var(--text-secondary);
    font-family: var(--font-body);
    font-size: var(--text-sm);
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition);
    text-decoration: none;
}

.lesson-nav-btn:hover {
    background: var(--bg-glass-hover);
    color: var(--text-primary);
    border-color: var(--border-hover);
    transform: translateY(-2px);
    text-decoration: none;
}

.lesson-nav-btn.primary {
    background: linear-gradient(135deg, var(--accent), var(--accent-dim));
    border-color: var(--accent);
    color: white;
}

.lesson-nav-btn.primary:hover {
    background: linear-gradient(135deg, var(--accent-bright), var(--accent));
    border-color: var(--accent-bright);
    box-shadow: 0 4px 20px rgba(79, 143, 247, 0.3);
}

.lesson-nav-btn.disabled,
.lesson-nav-btn:disabled {
    opacity: 0.35;
    cursor: not-allowed;
    pointer-events: none;
}

.lesson-nav-label {
    font-size: var(--text-xs);
    color: var(--text-muted);
    display: block;
    margin-bottom: 2px;
}

.lesson-nav-title {
    font-size: var(--text-sm);
}

/* ============================================================
   LESSON PAGES — Completion Overlay
   ============================================================ */
.lesson-complete-overlay {
    position: fixed;
    inset: 0;
    background: rgba(6, 10, 19, 0.9);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: var(--z-modal);
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-slow);
}

.lesson-complete-overlay.visible {
    opacity: 1;
    visibility: visible;
}

.lesson-complete-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-xl);
    padding: var(--space-12) var(--space-8);
    text-align: center;
    max-width: 440px;
    width: 90%;
    box-shadow: var(--shadow-xl);
    animation: scaleIn 0.5s ease;
    position: relative;
    overflow: hidden;
}

.lesson-complete-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--success), var(--accent-bright), var(--gold));
    background-size: 200% 100%;
    animation: shimmer 2s infinite linear;
}

.completion-icon {
    font-size: 4rem;
    margin-bottom: var(--space-4);
    display: block;
    animation: bounce 0.6s ease;
}

.completion-title {
    font-family: var(--font-display);
    font-size: var(--text-3xl);
    font-weight: 800;
    color: var(--text-primary);
    margin-bottom: var(--space-2);
}

.completion-subtitle {
    font-size: var(--text-base);
    color: var(--text-secondary);
    margin-bottom: var(--space-8);
    line-height: var(--leading-normal);
}

.completion-stats {
    display: flex;
    justify-content: center;
    gap: var(--space-8);
    margin-bottom: var(--space-8);
}

.completion-stat-value {
    font-family: var(--font-display);
    font-size: var(--text-2xl);
    font-weight: 700;
    color: var(--accent-bright);
}

.completion-stat-label {
    font-size: var(--text-xs);
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* --- Section Divider --- */
.section-divider {
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--border), transparent);
    margin: var(--space-10) 0;
}

/* --- Confetti --- */
.confetti-container {
    position: fixed;
    inset: 0;
    pointer-events: none;
    z-index: calc(var(--z-modal) + 1);
    overflow: hidden;
}

.confetti-piece {
    position: absolute;
    width: 10px;
    height: 10px;
    top: -10px;
    opacity: 0;
    animation: confettiFall var(--fall-duration, 3s) var(--fall-delay, 0s) ease-in forwards;
}

/* ============================================================
   LESSON PAGES — CTA Section (inside lessons)
   ============================================================ */
.lesson-cta-section {
    background: linear-gradient(135deg, var(--accent-glow), var(--gold-glow));
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: var(--space-8);
    text-align: center;
    margin: var(--space-8) 0;
}

.lesson-cta-section h3 {
    font-family: var(--font-display);
    font-size: var(--text-2xl);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--space-3);
}

.lesson-cta-section p {
    color: var(--text-secondary);
    margin-bottom: var(--space-5);
    line-height: var(--leading-normal);
}

/* ============================================================
   ANIMATIONS
   ============================================================ */
@keyframes shake {
    0%, 100% { transform: translateX(0); }
    10%, 50%, 90% { transform: translateX(-4px); }
    30%, 70% { transform: translateX(4px); }
}

@keyframes bounce {
    0% { transform: scale(0.5); }
    50% { transform: scale(1.15); }
    70% { transform: scale(0.95); }
    100% { transform: scale(1); }
}

@keyframes confettiFall {
    0% {
        opacity: 1;
        top: -10px;
        transform: translateX(0) rotateZ(0deg);
    }
    100% {
        opacity: 0;
        top: 100vh;
        transform: translateX(var(--drift, 80px)) rotateZ(var(--spin, 720deg));
    }
}

/* ============================================================
   RESPONSIVE — Tablet & Mobile
   ============================================================ */

/* --- Hub Responsive --- */
@media (max-width: 768px) {
    .course-hero {
        padding: calc(var(--space-20) + var(--space-4)) var(--space-4) var(--space-8);
    }

    .course-hero-title {
        font-size: var(--text-3xl);
    }

    .course-hero-subtitle {
        font-size: var(--text-base);
    }

    .lessons-section {
        padding: var(--space-4) var(--space-4) var(--space-12);
    }

    /* Mobile: card becomes horizontal row */
    .lesson-card {
        flex-direction: row;
        align-items: center;
        gap: var(--space-4);
        padding: var(--space-5) var(--space-4);
    }

    .lesson-card-number {
        position: static;
        flex-shrink: 0;
    }

    .lesson-card-icon {
        font-size: 2rem;
        margin: 0;
        flex-shrink: 0;
    }

    .lesson-card-body {
        flex: 1;
        min-width: 0;
    }

    .lesson-card-status {
        position: static;
        align-self: flex-start;
    }

    .lesson-card-footer {
        display: none;
    }

    .lesson-card-description {
        font-size: var(--text-xs);
    }

    .course-cta-card {
        padding: var(--space-8) var(--space-6);
    }

    .course-cta-title {
        font-size: var(--text-xl);
    }
}

@media (min-width: 769px) {
    .lesson-card-body {
        display: contents;
    }
}

/* --- Lesson Page Responsive --- */
@media (max-width: 768px) {
    .course-sidebar {
        transform: translateX(-100%);
    }

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

    .sidebar-overlay.open {
        display: block;
    }

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

    .hamburger-btn {
        display: block;
    }

    .lesson-content {
        padding: var(--space-6) var(--space-4) var(--space-12);
    }

    .lesson-title {
        font-size: var(--text-2xl);
    }

    .lesson-subtitle {
        font-size: var(--text-xl);
    }

    .board-with-panel {
        flex-direction: column;
    }

    .board-with-panel .board-side {
        flex: 0 0 auto;
        width: 100%;
    }

    .exercise-board-area {
        width: min(320px, 80vw, 45vh);
    }

    .lesson-nav {
        flex-direction: column;
        gap: var(--space-4);
    }

    .lesson-nav-btn {
        width: 100%;
        justify-content: center;
    }

    .completion-stats {
        gap: var(--space-5);
    }
}

/* --- Small phones --- */
@media (max-width: 480px) {
    .lesson-header {
        padding: 0 var(--space-4);
    }

    .lesson-content {
        padding: var(--space-5) var(--space-4) var(--space-10);
    }

    .lesson-title {
        font-size: var(--text-xl);
    }

    .lesson-subtitle {
        font-size: var(--text-lg);
    }

    .lesson-text {
        font-size: var(--text-sm);
    }

    .board-container {
        width: min(300px, 85vw, 42vh);
    }

    .exercise-board-area {
        width: min(300px, 85vw, 42vh);
    }

    .exercise-card {
        padding: var(--space-5) var(--space-4);
    }

    .exercise-instruction {
        font-size: var(--text-sm);
        padding: var(--space-3) var(--space-4);
    }

    .exercise-buttons {
        flex-direction: column;
    }

    .exercise-btn {
        width: 100%;
        justify-content: center;
    }

    .lesson-complete-card {
        padding: var(--space-8) var(--space-6);
    }

    .completion-title {
        font-size: var(--text-xl);
    }

    .concept-box,
    .tip-box,
    .warning-box {
        padding: var(--space-4) var(--space-5);
    }

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

/* ============================================================
   LARGE SCREENS
   ============================================================ */
@media (min-width: 1400px) {
    .lesson-content {
        max-width: 960px;
    }
}

/* ============================================================
   CHESS BOARD — Global Fallback
   ============================================================ */
chess-board {
    --light-color: var(--board-light);
    --dark-color: var(--board-dark);
    --highlight-color: var(--board-highlight);
}

chess-board::part(notation) {
    font-size: 0.55rem;
}

chess-board::part(alpha),
chess-board::part(numeric) {
    font-size: 0.55rem;
    opacity: 0.7;
}

/* ============================================================
   PRINT STYLES
   ============================================================ */
@media print {
    .course-sidebar,
    .hamburger-btn,
    .sidebar-overlay,
    .lesson-progress,
    .exercise-buttons,
    .lesson-nav,
    .lesson-complete-overlay {
        display: none !important;
    }

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

    body {
        background: white;
        color: black;
    }
}