/* learn page layout, sections, and navigation
   extracted from styles.css -- do not duplicate in the source file */

/* prevent flash of unstyled content while lesson-stepper restructures DOM */
body.learn-loading {
    opacity: 0;
}
body.learn-ready {
    opacity: 1;
    transition: opacity 0.12s ease;
}

/* ============================================== */
/* Learn page styles */
/* ============================================== */

.learn-page {
    padding-top: 80px;
}

html {
    scroll-padding-top: 88px;
}

.breadcrumb {
    font-size: 0.78rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-md);
    display: flex;
    align-items: center;
    gap: 8px;
}

.breadcrumb a {
    color: var(--color-text-muted);
    text-decoration: none;
    transition: color var(--transition-fast);
}

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

.breadcrumb svg {
    width: 12px;
    height: 12px;
}

.breadcrumb-sep {
    opacity: 0.4;
}

.learn-header {
    margin-bottom: var(--spacing-lg);
}

.learn-module-badge {
    display: inline-block;
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-primary);
    padding: 0.2rem 0.6rem;
    background: rgba(52, 211, 153, 0.08);
    border-radius: 4px;
    margin-bottom: 0.5rem;
}

.learn-title {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 16px;
    color: var(--color-text);
    line-height: 1.15;
}

.learn-subtitle {
    font-size: 1rem;
    color: var(--color-text-muted);
    max-width: 640px;
    line-height: 1.7;
}

/* next module CTA */
.learn-next {
    text-align: center;
    padding: var(--spacing-xl) 0;
    border-top: 1px solid var(--color-border);
    margin-top: var(--spacing-lg);
}

.learn-next-label {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-text-muted);
    margin-bottom: 0.5rem;
}

/* ============================================== */
/* Hero section (learn pages only) */
/* ============================================== */

.learn-page .hero {
    padding: var(--spacing-lg) 0 var(--spacing-md);
    min-height: auto;
    display: block;
    position: static;
}

.learn-page .hero-title {
    font-size: 1.75rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 16px;
    color: var(--color-text);
    line-height: 1.15;
}

@media (min-width: 768px) {
    .learn-page .hero-title {
        font-size: 2.4rem;
    }
}

.learn-page .hero-stat {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    background: rgba(52, 211, 153, 0.06);
    border: 1px solid rgba(52, 211, 153, 0.15);
    border-radius: 20px;
    font-size: 0.85rem;
    color: var(--color-primary);
    font-weight: 500;
    margin-bottom: var(--spacing-sm);
}

.learn-page .hero-description {
    color: var(--color-text-muted);
    font-size: 0.95rem;
    max-width: 640px;
    line-height: 1.8;
}

@media (min-width: 768px) {
    .learn-page .hero-description {
        font-size: 0.95rem;
    }
}

/* ============================================== */
/* Narrative sections */
/* ============================================== */

.narrative-section {
    margin-bottom: var(--spacing-lg);
}

.section-intro {
    margin-bottom: var(--spacing-md);
}

.section-title {
    font-size: 1.35rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: 16px;
    color: var(--color-text);
}

@media (min-width: 768px) {
    .section-title {
        font-size: 1.35rem;
    }
}

.section-description {
    color: var(--color-text-muted);
    font-size: 0.95rem;
    line-height: 1.8;
    margin-bottom: 16px;
}

@media (min-width: 768px) {
    .section-description {
        font-size: 0.95rem;
    }
}

.section-description strong {
    color: var(--color-text);
}

/* section divider */
.section-divider {
    border: none;
    height: 1px;
    background: linear-gradient(to right, transparent, var(--color-border) 20%, var(--color-border) 80%, transparent);
    margin: var(--spacing-lg) auto;
    max-width: 150px;
}

@media (min-width: 768px) {
    .section-divider {
        margin: var(--spacing-xl) auto;
        max-width: 200px;
    }
}

/* ============================================== */
/* Entrance animations */
/* ============================================== */

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(24px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeInScale {
    from {
        opacity: 0;
        transform: scale(0.95);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

.animate-on-scroll {
    opacity: 0;
    transform: translateY(24px);
    transition: opacity var(--transition-slow),
                transform var(--transition-slow);
}

.animate-on-scroll.is-visible {
    opacity: 1;
    transform: translateY(0);
}

/* stagger children within grids */
.animate-on-scroll.is-visible .card {
    animation: fadeInScale 0.5s cubic-bezier(0.25, 0.1, 0.25, 1) both;
}

.animate-on-scroll.is-visible .card:nth-child(1) { animation-delay: 0ms; }
.animate-on-scroll.is-visible .card:nth-child(2) { animation-delay: 80ms; }
.animate-on-scroll.is-visible .card:nth-child(3) { animation-delay: 160ms; }
.animate-on-scroll.is-visible .card:nth-child(4) { animation-delay: 240ms; }
.animate-on-scroll.is-visible .card:nth-child(5) { animation-delay: 320ms; }
.animate-on-scroll.is-visible .card:nth-child(6) { animation-delay: 400ms; }

/* respect reduced motion */
@media (prefers-reduced-motion: reduce) {
    .animate-on-scroll {
        opacity: 1;
        transform: none;
        transition: none;
    }

    .animate-on-scroll.is-visible .card {
        animation: none;
    }
}

/* noscript fallback */
.no-js .animate-on-scroll {
    opacity: 1;
    transform: none;
}

/* ============================================== */
/* Card - glassmorphic container */
/* ============================================== */

.card {
    background: rgba(255, 255, 255, 0.6);
    backdrop-filter: blur(8px) saturate(150%);
    -webkit-backdrop-filter: blur(8px) saturate(150%);
    border: 1px solid rgba(255, 255, 255, 0.5);
    border-radius: var(--radius);
    padding: var(--spacing-sm);
    box-shadow:
        var(--shadow-sm),
        inset 0 1px 0 rgba(255, 255, 255, 0.6);
    transition: box-shadow var(--transition-smooth), transform var(--transition-smooth);
}

@media (min-width: 768px) {
    .card {
        padding: var(--spacing-md);
    }
}

.card:hover {
    box-shadow:
        var(--shadow-md),
        inset 0 1px 0 rgba(255, 255, 255, 0.6);
    transform: translateY(-2px);
}

.card-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 0.75rem;
}

@media (min-width: 768px) {
    .card-header {
        margin-bottom: 1rem;
    }
}

.card-header h3 {
    font-size: 1rem;
    font-weight: 600;
    text-transform: lowercase;
}

@media (min-width: 768px) {
    .card-header h3 {
        font-size: 1.125rem;
    }
}

/* ============================================== */
/* Card grids */
/* ============================================== */

.card-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-sm);
}

.course-comparison-grid {
    margin-top: var(--spacing-md);
}

.course-comparison-title {
    font-size: 0.95rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    text-transform: lowercase;
    color: var(--color-text);
}

.course-comparison-meta {
    font-size: 0.82rem;
    color: var(--color-text-muted);
    margin-bottom: 0.35rem;
}

.course-comparison-kicker {
    font-size: 0.72rem;
    color: var(--color-primary);
    margin-bottom: 0.35rem;
    font-weight: 600;
}

.course-comparison-desc {
    font-size: 0.82rem;
    color: var(--color-text-muted);
    line-height: 1.55;
}

.course-comparison-desc--tight {
    line-height: 1.5;
}

.course-year-tag {
    font-size: 0.72rem;
    font-weight: 600;
    margin-bottom: 0.35rem;
}

.course-year-tag--primary {
    color: var(--color-primary);
}

.course-year-tag--success {
    color: var(--color-success);
}

.course-year-tag--warning {
    color: var(--color-warning);
}

.course-year-tag--danger {
    color: var(--color-danger);
}

.regulatory-card-copy {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    line-height: 1.5;
}

.course-link-row {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    margin-top: 16px;
}

.course-link-chip {
    display: inline-flex;
    align-items: baseline;
    gap: 8px;
    padding: 16px 24px;
    text-decoration: none;
    color: var(--color-text);
}

.course-link-chip-sub {
    opacity: 0.7;
    font-size: 0.9em;
    text-transform: lowercase;
}

.btn-top-gap {
    margin-top: 1rem;
}

.course-grid--narrow {
    max-width: 700px;
    margin: 0 auto;
}

.content-hidden {
    display: none;
}

.routes-grid {
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
}

.route-card {
    text-align: center;
}

.route-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 2.1rem;
    padding: 0.18rem 0.45rem;
    margin-bottom: 0.35rem;
    font-size: 0.78rem;
    line-height: 1;
    font-weight: 700;
    text-transform: uppercase;
    border-radius: 999px;
    border: 1px solid rgba(52, 211, 153, 0.3);
    background: rgba(52, 211, 153, 0.1);
    color: var(--color-primary);
}

.route-name {
    font-size: 0.85rem;
    font-weight: 600;
    text-transform: lowercase;
}

.route-metric {
    font-size: 0.72rem;
    color: var(--color-text-muted);
}

.route-note {
    font-size: 0.7rem;
    color: var(--color-text-muted);
    margin-top: 0.25rem;
}

.calculator-result-panel {
    margin-top: 0.5rem;
    padding: 0.75rem;
    background: var(--color-disabled-bg);
    border-radius: var(--radius);
}

.calculator-result-label {
    font-size: 0.82rem;
    color: var(--color-text-muted);
    margin-bottom: 0.35rem;
}

.calculator-result-label--spaced {
    margin-top: 0.5rem;
}

.calculator-result-value {
    font-size: 1.25rem;
    font-weight: 700;
    font-family: var(--font-mono);
}

.calculator-vial-svg {
    width: 160px;
    height: auto;
}

.icon-sm {
    width: 14px;
    height: 14px;
}

.icon-md {
    width: 16px;
    height: 16px;
}

@media (min-width: 600px) {
    .card-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-md);
    }
}

@media (min-width: 900px) {
    .card-grid.grid-3 {
        grid-template-columns: repeat(3, 1fr);
    }
}

/* ============================================== */
/* Spectrum / slider visualization */
/* ============================================== */

.spectrum-bar {
    height: 6px;
    border-radius: 3px;
    background: linear-gradient(to right, var(--color-primary), var(--color-success), var(--color-warning));
    position: relative;
    margin: var(--spacing-md) 0;
}

.spectrum-labels {
    display: flex;
    justify-content: space-between;
    font-size: 0.72rem;
    color: var(--color-text-muted);
    margin-top: 0.35rem;
}

/* ============================================== */
/* Lesson sidebar */
/* ============================================== */

/* wider container when sidebar is present */
.learn-page--with-sidebar {
    max-width: none;
    margin: 0;
    padding: 0;
}

/* flex layout: sidebar + content */
.learn-layout {
    display: flex;
    gap: 0;
    position: relative;
    min-height: 100vh;
}

/* main content area */
.learn-content {
    flex: 1;
    min-width: 0;
    max-width: 900px;
    margin: 0 auto;
    padding: var(--spacing-lg) var(--spacing-md);
    display: flex;
    flex-direction: column;
}

/* sidebar container */
.lesson-sidebar {
    position: relative;
    flex-shrink: 0;
    z-index: var(--z-stepper);
    min-width: 48px;
    transition: min-width 0.3s cubic-bezier(0.25, 0.1, 0.25, 1);
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    border-right: 1px solid var(--glass-border);
}

/* shrink sidebar container when panel is collapsed */
.lesson-sidebar:has(.sidebar-panel-collapsed) {
    min-width: 0;
    width: 0;
    border-right-color: transparent;
    background: transparent;
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
}

/* sidebar toggle button (lives inside sidebar title area) */
.sidebar-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-surface);
    color: var(--color-text-muted);
    cursor: pointer;
    transition: all 0.2s ease;
    flex-shrink: 0;
}

.sidebar-toggle:hover {
    border-color: var(--color-primary);
    color: var(--color-text);
}

/* reopen button: visible only when sidebar panel is collapsed */
.sidebar-reopen {
    display: none;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-surface);
    color: var(--color-text-muted);
    cursor: pointer;
    transition: all 0.2s ease;
    flex-shrink: 0;
    position: fixed;
    top: calc(var(--stepper-nav-offset, 84px) + 8px);
    left: 8px;
    z-index: var(--z-stepper-reopen);
    margin: 0;
}

.sidebar-reopen:hover {
    border-color: var(--color-primary);
    color: var(--color-text);
}

.sidebar-panel-collapsed ~ .sidebar-reopen {
    display: flex;
}

/* sidebar panel */
.sidebar-panel {
    position: sticky;
    top: 80px;
    height: calc(100vh - 80px);
    width: 260px;
    overflow-y: auto;
    padding: var(--spacing-lg) var(--spacing-sm) var(--spacing-lg);
    border-right: none;
    background: transparent;
    transition: width 0.3s cubic-bezier(0.25, 0.1, 0.25, 1),
                padding 0.3s cubic-bezier(0.25, 0.1, 0.25, 1),
                opacity 0.25s ease;
    scrollbar-width: thin;
    scrollbar-color: var(--color-border) transparent;
}

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

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

/* collapsed state */
.sidebar-panel-collapsed {
    width: 0;
    padding-left: 0;
    padding-right: 0;
    overflow: hidden;
    opacity: 0;
}

/* ── sidebar module header ── */
.sidebar-module-header {
    padding: 0 0.25rem;
    margin-bottom: var(--spacing-sm);
}

.sidebar-module-header-top {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 0.5rem;
}

.sidebar-module-header-top .sidebar-toggle {
    position: relative;
    top: auto;
    left: auto;
    margin: 0;
    flex-shrink: 0;
}

.sidebar-unit-badge {
    font-size: 0.65rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-text-muted);
    background: var(--color-disabled-bg);
    padding: 0.2rem 0.55rem;
    border-radius: 999px;
}

.sidebar-module-title {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--color-text);
    margin: 0;
    letter-spacing: -0.02em;
    line-height: 1.3;
}

/* ── sidebar meta (lesson count + progress %) ── */
.sidebar-meta {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--spacing-xs);
    padding: 0 0.25rem;
    white-space: nowrap;
}

.sidebar-meta-label {
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-muted);
}

.sidebar-meta-pct {
    font-size: 0.7rem;
    font-weight: 600;
    color: var(--color-primary);
    font-family: var(--font-mono);
}

/* sidebar progress bar */
.sidebar-progress {
    height: 3px;
    background: var(--color-border);
    border-radius: 2px;
    margin-bottom: var(--spacing-md);
    overflow: hidden;
}

.sidebar-progress-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--color-primary), var(--color-success));
    border-radius: 2px;
    transition: width 0.4s ease;
}

/* step list */
.sidebar-steps {
    display: flex;
    flex-direction: column;
    gap: 2px;
}

/* individual step */
.sidebar-step {
    display: flex;
    align-items: center;
    gap: 0.55rem;
    width: 100%;
    padding: 0.5rem 0.55rem;
    border: none;
    border-radius: var(--radius);
    background: transparent;
    color: var(--color-text-muted);
    font-size: 0.78rem;
    font-family: var(--font-sans);
    font-weight: 400;
    cursor: pointer;
    text-align: left;
    transition: all 0.15s ease;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    position: relative;
}

.sidebar-step:hover {
    background: rgba(255, 255, 255, 0.04);
    color: var(--color-text);
}

/* active step */
.sidebar-step-active {
    background: rgba(52, 211, 153, 0.08);
    color: var(--color-primary);
    font-weight: 600;
}

.sidebar-step-active:hover {
    background: rgba(52, 211, 153, 0.12);
}

html.dark .sidebar-step-active {
    background: rgba(52, 211, 153, 0.1);
}

html.dark .sidebar-step-active:hover {
    background: rgba(52, 211, 153, 0.15);
}

.sidebar-step-active::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0.3rem;
    bottom: 0.3rem;
    width: 3px;
    border-radius: 0 2px 2px 0;
    background: var(--color-primary);
}

.sidebar-step-active .sidebar-step-icon {
    color: var(--color-primary);
    background: rgba(52, 211, 153, 0.15);
}

html.dark .sidebar-step-active .sidebar-step-icon {
    background: rgba(52, 211, 153, 0.18);
}

/* completed step */
.sidebar-step-complete {
    color: var(--color-text-muted);
}

.sidebar-step-complete .sidebar-step-icon {
    color: var(--color-success);
    background: rgba(16, 185, 129, 0.12);
}

.sidebar-step-complete.sidebar-step-active {
    color: var(--color-success);
}

.sidebar-step-complete.sidebar-step-active::before {
    background: var(--color-success);
}

.sidebar-step-complete.sidebar-step-active .sidebar-step-icon {
    background: rgba(16, 185, 129, 0.18);
}

/* step icon */
.sidebar-step-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    flex-shrink: 0;
    border-radius: 50%;
    background: var(--color-border);
    transition: background 0.15s ease;
}

.stepper-num {
    font-size: 0.65rem;
    font-weight: 600;
}

/* step label */
.sidebar-step-label {
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    flex: 1;
}

/* step type tags */
.sidebar-step-tag {
    font-size: 0.58rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.03em;
    padding: 0.1rem 0.3rem;
    border-radius: 3px;
    flex-shrink: 0;
}

.sidebar-step-tag--quiz {
    background: rgba(52, 211, 153, 0.1);
    color: var(--color-primary);
}

.sidebar-step-tag--exercise {
    background: rgba(249, 115, 22, 0.1);
    color: #f97316;
}

/* backdrop for mobile overlay */
.sidebar-backdrop {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: var(--z-stepper-backdrop);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease;
}

/* ── course directory (migrated from injected styles) ── */

.sidebar-divider {
    height: 1px;
    background: linear-gradient(to right, transparent, var(--color-border) 20%, var(--color-border) 80%, transparent);
    margin: var(--spacing-md) 0.25rem var(--spacing-sm);
}

.sidebar-units-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 0.55rem;
    margin-bottom: 0.35rem;
}

.sidebar-units-label {
    font-size: 0.68rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-text-muted);
}

.sidebar-units {
    display: flex;
    flex-direction: column;
    gap: 2px;
    margin-bottom: var(--spacing-sm);
}

.sidebar-unit-link {
    display: flex;
    align-items: center;
    gap: 0.55rem;
    width: 100%;
    padding: 0.45rem 0.55rem;
    border: none;
    border-radius: var(--radius);
    background: transparent;
    color: var(--color-text-muted);
    font-size: 0.75rem;
    text-decoration: none;
    transition: all 0.15s ease;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    position: relative;
}

.sidebar-unit-link:hover {
    background: rgba(255, 255, 255, 0.04);
    color: var(--color-text);
}

.sidebar-unit-link-active {
    color: var(--color-text);
    font-weight: 600;
    background: rgba(52, 211, 153, 0.06);
}

.sidebar-unit-link-active:hover {
    background: rgba(52, 211, 153, 0.08);
}

/* locked unit -- non-interactive */
.sidebar-unit-link--locked {
    cursor: default;
    opacity: 0.45;
}

.sidebar-unit-link--locked:hover {
    background: transparent;
    color: var(--color-text-muted);
    opacity: 0.6;
}

.sidebar-unit-num {
    font-size: 0.65rem;
    font-weight: 700;
    font-family: var(--font-mono);
    opacity: 0.5;
    min-width: 1.2rem;
}

.sidebar-unit-status {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 18px;
    height: 18px;
    flex-shrink: 0;
    opacity: 0.6;
    margin-left: auto;
}

/* locked tooltip */
.sidebar-unit-tooltip {
    position: absolute;
    left: 0.55rem;
    top: 100%;
    z-index: 10;
    background: var(--glass-bg);
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius);
    padding: 0.45rem 0.65rem;
    white-space: nowrap;
    font-size: 0.7rem;
    color: var(--color-text);
    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.15);
    animation: tooltipFadeIn 0.2s ease;
    pointer-events: auto;
}

.sidebar-unit-tooltip a {
    color: var(--color-primary);
    text-decoration: none;
    font-weight: 600;
}

.sidebar-unit-tooltip a:hover {
    text-decoration: underline;
}

@keyframes tooltipFadeIn {
    from {
        opacity: 0;
        transform: translateY(-4px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* unlock CTA at bottom of course units */
.sidebar-unlock-cta {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.5rem 0.55rem;
    margin-top: 0.25rem;
    border-radius: var(--radius);
    font-size: 0.72rem;
    font-weight: 600;
    color: var(--color-primary);
    text-decoration: none;
    transition: all 0.2s ease;
}

.sidebar-unlock-cta:hover {
    background: rgba(52, 211, 153, 0.08);
}

.sidebar-unlock-cta svg {
    width: 12px;
    height: 12px;
}

/* dark mode glassmorphism */
html.dark .lesson-sidebar {
    background: rgba(13, 13, 13, 0.85);
    backdrop-filter: blur(24px) saturate(200%);
    -webkit-backdrop-filter: blur(24px) saturate(200%);
    border-right-color: rgba(255, 255, 255, 0.07);
}

html.dark .lesson-sidebar:has(.sidebar-panel-collapsed) {
    background: transparent;
    border-right-color: transparent;
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
}

html.dark .sidebar-toggle {
    background: rgba(24, 24, 28, 0.9);
    border-color: rgba(255, 255, 255, 0.08);
}

html.dark .sidebar-unit-tooltip {
    background: rgba(24, 24, 28, 0.95);
    border-color: rgba(255, 255, 255, 0.1);
    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.4);
}

/* lesson bottom navigation */

.lesson-nav {
    margin-top: auto;
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--color-border);
}

.lesson-nav-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--spacing-sm);
}

.lesson-nav-btn {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.6rem 1rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-surface);
    color: var(--color-text);
    font-size: 0.82rem;
    font-family: var(--font-sans);
    cursor: pointer;
    transition: all 0.2s ease;
    text-decoration: none;
}

.lesson-nav-btn:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

.lesson-nav-next {
    background: var(--color-primary);
    border-color: var(--color-primary);
    color: #fff;
}

.lesson-nav-next:hover {
    background: var(--color-primary-hover);
    border-color: var(--color-primary-hover);
    color: #fff;
}

.lesson-nav-next-module {
    background: var(--color-success);
    border-color: var(--color-success);
}

.lesson-nav-next-module:hover {
    background: #059669;
    border-color: #059669;
    color: #fff;
}

.lesson-nav-counter {
    font-size: 0.75rem;
    color: var(--color-text-muted);
    font-family: var(--font-mono);
}

/* responsive sidebar + nav */

@media (max-width: 900px) {
    .learn-layout {
        display: block;
    }

    .lesson-sidebar {
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        z-index: var(--z-stepper-panel);
        pointer-events: none;
        min-width: 0;
    }

    /* on mobile, reopen button is fixed and always visible (acts as open trigger) */
    .sidebar-reopen {
        display: flex;
        position: fixed;
        top: 72px;
        left: var(--spacing-xs);
        z-index: var(--z-stepper-nav);
        pointer-events: auto;
        margin: 0;
    }

    /* hide the CSS-only sibling rule on mobile; JS handles visibility */
    .sidebar-panel-collapsed ~ .sidebar-reopen {
        display: flex;
    }

    .sidebar-panel:not(.sidebar-panel-collapsed) ~ .sidebar-reopen {
        display: none;
    }

    .sidebar-panel {
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        height: 100%;
        width: 280px;
        padding-top: 80px;
        transform: translateX(-100%);
        z-index: var(--z-stepper-backdrop-mobile);
        opacity: 1;
        background: var(--color-surface);
        backdrop-filter: blur(24px) saturate(180%);
        -webkit-backdrop-filter: blur(24px) saturate(180%);
        border-right: 1px solid var(--glass-border);
        box-shadow: 4px 0 32px rgba(0, 0, 0, 0.2);
        pointer-events: auto;
        overflow: hidden;
    }

    html.dark .sidebar-panel {
        background: rgba(13, 13, 13, 0.95);
    }

    .lesson-sidebar {
        background: transparent;
        border-right: none;
        backdrop-filter: none;
        -webkit-backdrop-filter: none;
    }

    .sidebar-panel-collapsed {
        width: 280px;
        padding: var(--spacing-md) var(--spacing-sm) var(--spacing-lg);
        padding-top: 80px;
        opacity: 1;
        transform: translateX(-100%);
        overflow: hidden;
    }

    .sidebar-panel:not(.sidebar-panel-collapsed) {
        transform: translateX(0);
        overflow-y: auto;
    }

    .sidebar-backdrop {
        display: block;
    }

    body.sidebar-overlay-open .sidebar-backdrop {
        opacity: 1;
        pointer-events: auto;
    }

    body.sidebar-overlay-open .lesson-sidebar {
        pointer-events: auto;
    }

    .sidebar-step-label {
        white-space: normal;
    }

    .lesson-nav-btn span {
        max-width: 120px;
        overflow: hidden;
        text-overflow: ellipsis;
        white-space: nowrap;
    }
}

@media (max-width: 480px) {
    .lesson-nav-btn {
        padding: 0.5rem 0.65rem;
        font-size: 0.75rem;
    }

    .lesson-nav-btn span {
        max-width: 80px;
    }
}

/* reduced motion */
@media (prefers-reduced-motion: reduce) {
    .sidebar-panel,
    .sidebar-step,
    .sidebar-toggle,
    .sidebar-progress-bar,
    .sidebar-backdrop,
    .sidebar-unit-link {
        transition: none;
    }

    .sidebar-unit-tooltip {
        animation: none;
    }
}

/* tighter footer on learn pages with sidebar */
.learn-page--with-sidebar ~ .landing-footer {
    margin-top: 0;
    padding-top: 48px;
}