/* ============================================================
   clojure-cert — Neon Nubank Purple & Silver Theme
   Dark = original cyber-night.  Light = brushed silver + neon.
   ============================================================ */

:root {
    --font-ui:    'Inter', system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
    --font-mono:  'JetBrains Mono', 'Fira Code', 'Cascadia Code', Menlo, Consolas, monospace;
}

:root, [data-theme="dark"] {
    --bg-base:           #0b0814;
    --bg-deep:           #0e0a1d;
    --bg-primary:        #0b0814;
    --bg-secondary:      #110d22;
    --bg-card:           rgba(22, 16, 38, 0.74);
    --bg-elevated:       rgba(28, 22, 48, 0.82);
    --code-bg:           #0a0716;

    --metal-1:           #2e2842;
    --metal-2:           #3e3658;
    --metal-3:           #5d5478;
    --metal-light-1:     #c6bdda;
    --metal-light-2:     #ddd5ec;
    --metal-edge:        rgba(225, 218, 245, 0.18);

    --purple-neon:       #b87fff;
    --purple-glow:       rgba(184, 127, 255, 0.55);
    --purple-soft:       rgba(184, 127, 255, 0.18);
    --purple-deep:       #6e2caf;
    --purple-text:       #d6b4ff;

    --text-primary:      #e6dcf2;
    --text-secondary:    #9d92b6;
    --text-muted:        #6f6587;

    --border:            rgba(184, 127, 255, 0.16);
    --border-strong:     rgba(184, 127, 255, 0.36);

    --success:           #39ff9c;
    --success-glow:      rgba(57, 255, 156, 0.40);
    --danger:            #ff4d6d;
    --danger-glow:       rgba(255, 77, 109, 0.40);
    --warning:           #ffd56b;

    /* Diff colors — kept semantic regardless of theme */
    --diff-add:          #39ff9c;
    --diff-rem:          #ff4d6d;

    --accent:            #b87fff;
    --accent-hover:      #d6b4ff;

    --shadow-glow:       0 0 32px rgba(184, 127, 255, 0.18);
    --shadow-deep:       0 12px 48px rgba(0, 0, 0, 0.55);

    /* Theme-specific composites */
    --backdrop:
        radial-gradient(ellipse 70% 50% at 30% 0%, rgba(184, 127, 255, 0.12), transparent 60%),
        radial-gradient(ellipse 50% 40% at 80% 100%, rgba(214, 180, 255, 0.05), transparent 65%),
        linear-gradient(180deg, #0d0820 0%, #0b0814 60%, #0b0814 100%);
    --header-bg:         linear-gradient(180deg, rgba(28, 22, 48, 0.7), rgba(14, 10, 28, 0.85));
    --card-bg:           linear-gradient(160deg, rgba(28, 22, 48, 0.85), rgba(14, 10, 28, 0.95));
    --hover-shadow:      0 12px 32px rgba(0, 0, 0, 0.5);
    --result-success-bg: rgba(57, 255, 156, 0.07);
    --result-failure-bg: rgba(255, 77, 109, 0.07);
    --title-gradient:    linear-gradient(135deg, #ffffff 0%, var(--purple-text) 50%, var(--purple-neon) 100%);
    --btn-shadow:        inset 0 1px 0 rgba(255,255,255,0.06), 0 2px 6px rgba(0,0,0,0.4);
    --btn-primary-shadow:
        inset 0 1px 0 rgba(255,255,255,0.4),
        0 0 18px var(--purple-glow),
        0 6px 18px rgba(0,0,0,0.4);

    --sidebar-bg:        rgba(14, 10, 28, 0.78);
    --sidebar-header-bg: rgba(28, 22, 48, 0.6);
    --hover-bg:          rgba(184, 127, 255, 0.06);
    --hover-bg-strong:   rgba(184, 127, 255, 0.12);
    --accent-bg:         rgba(184, 127, 255, 0.12);
}

[data-theme="light"] {
    --bg-base:           #e8e2f0;
    --bg-deep:           #d4cce0;
    --bg-primary:        #e8e2f0;
    --bg-secondary:      #ede8f4;
    --bg-card:           rgba(255, 255, 255, 0.78);
    --bg-elevated:       rgba(255, 255, 255, 0.92);
    --code-bg:           #1c1530;

    --metal-1:           #c0b6cf;
    --metal-2:           #d2cadd;
    --metal-3:           #e1dbeb;
    --metal-light-1:     #6c5e87;
    --metal-light-2:     #574a72;
    --metal-edge:        rgba(60, 40, 90, 0.20);

    --purple-neon:       #820ad1;
    --purple-glow:       rgba(130, 10, 209, 0.40);
    --purple-soft:       rgba(130, 10, 209, 0.14);
    --purple-deep:       #51067a;
    --purple-text:       #6e08aa;

    --text-primary:      #221530;
    --text-secondary:    #4a3d5e;
    --text-muted:        #756689;

    --border:            rgba(130, 10, 209, 0.22);
    --border-strong:     rgba(130, 10, 209, 0.50);

    --success:           #1a7d40;
    --success-glow:      rgba(26, 125, 64, 0.30);
    --danger:            #b32639;
    --danger-glow:       rgba(179, 38, 57, 0.30);
    --warning:           #b58410;

    --diff-add:          #1a7d40;
    --diff-rem:          #b32639;

    --accent:            #820ad1;
    --accent-hover:      #6e08aa;

    --shadow-glow:       0 0 24px rgba(130, 10, 209, 0.18);
    --shadow-deep:       0 8px 28px rgba(60, 40, 90, 0.20);

    --backdrop:
        radial-gradient(ellipse 70% 50% at 30% 0%, rgba(130, 10, 209, 0.10), transparent 60%),
        radial-gradient(ellipse 50% 40% at 80% 100%, rgba(110, 8, 170, 0.05), transparent 65%),
        linear-gradient(180deg, #f0eaf6 0%, #e8e2f0 60%, #ddd4ea 100%);
    --header-bg:         linear-gradient(180deg, rgba(255, 255, 255, 0.85), rgba(232, 226, 240, 0.90));
    --card-bg:           linear-gradient(160deg, rgba(255, 255, 255, 0.95), rgba(240, 232, 248, 0.92));
    --hover-shadow:      0 12px 28px rgba(60, 40, 90, 0.22);
    --result-success-bg: rgba(26, 125, 64, 0.08);
    --result-failure-bg: rgba(179, 38, 57, 0.08);
    --title-gradient:    linear-gradient(135deg, var(--text-primary) 0%, var(--purple-deep) 50%, var(--purple-neon) 100%);
    --btn-shadow:        inset 0 1px 0 rgba(255,255,255,0.7), 0 2px 6px rgba(60,40,90,0.18);
    --btn-primary-shadow:
        inset 0 1px 0 rgba(255,255,255,0.5),
        0 0 14px var(--purple-glow),
        0 4px 12px rgba(60, 40, 90, 0.20);

    --sidebar-bg:        rgba(255, 255, 255, 0.82);
    --sidebar-header-bg: rgba(240, 232, 248, 0.65);
    --hover-bg:          rgba(130, 10, 209, 0.07);
    --hover-bg-strong:   rgba(130, 10, 209, 0.14);
    --accent-bg:         rgba(130, 10, 209, 0.14);
}

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

html, body {
    min-height: 100vh;
    background: var(--bg-base);
    color: var(--text-primary);
    font-family: var(--font-ui);
    font-size: 14px;
    line-height: 1.55;
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
    transition: background-color 0.3s ease, color 0.3s ease;
}

body::before {
    content: '';
    position: fixed;
    inset: 0;
    z-index: -2;
    background: var(--backdrop);
    transition: background 0.3s ease;
}
body::after {
    content: '';
    position: fixed;
    inset: 0;
    z-index: -1;
    background-image:
        linear-gradient(var(--border) 1px, transparent 1px),
        linear-gradient(90deg, var(--border) 1px, transparent 1px);
    background-size: 48px 48px;
    mask-image: radial-gradient(ellipse 80% 60% at 50% 30%, black 30%, transparent 80%);
    -webkit-mask-image: radial-gradient(ellipse 80% 60% at 50% 30%, black 30%, transparent 80%);
    animation: gridDrift 60s linear infinite;
    opacity: 0.6;
}
@keyframes gridDrift {
    from { background-position: 0 0, 0 0; }
    to   { background-position: 48px 48px, 48px 48px; }
}
@keyframes pulse {
    0%, 100% { opacity: 1; }
    50%      { opacity: 0.55; }
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 20px;
}

/* Header */
.header {
    background: var(--header-bg);
    border-bottom: 1px solid var(--border);
    padding: 22px 0;
    margin-bottom: 30px;
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: background 0.3s ease, border-color 0.3s ease;
}

.header .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
    max-width: none;
    margin: 0;
    padding: 0 24px;
}

.header-titles {
    display: flex;
    flex-direction: column;
    gap: 4px;
    min-width: 0;
}

.header-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 16px;
}

.header-actions {
    display: flex;
    align-items: center;
    gap: 10px;
    flex-shrink: 0;
}

.header h1 {
    font-size: 1.75rem;
    font-weight: 700;
    letter-spacing: -0.01em;
    display: flex;
    align-items: center;
    gap: 14px;
    background: var(--title-gradient);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}
.header h1::before {
    content: '';
    width: 36px; height: 36px;
    border-radius: 10px;
    background: conic-gradient(from 220deg, var(--purple-neon), var(--purple-deep), var(--metal-2), var(--purple-neon));
    box-shadow:
        0 0 22px var(--purple-glow),
        inset 0 0 0 1px var(--metal-edge);
    flex-shrink: 0;
    -webkit-background-clip: border-box;
    background-clip: border-box;
}

.header .subtitle {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-left: 50px;
    display: block;
}

/* Theme Toggle */
.theme-toggle {
    position: relative;
    width: 56px;
    height: 28px;
    background: var(--bg-deep);
    border: 1px solid var(--border-strong);
    border-radius: 14px;
    cursor: pointer;
    padding: 0;
    flex-shrink: 0;
    transition: all 0.2s ease;
}
.theme-toggle:hover {
    border-color: var(--purple-neon);
    box-shadow: 0 0 14px var(--purple-soft);
}
.theme-toggle::before, .theme-toggle::after {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    font-size: 11px;
    color: var(--text-muted);
    pointer-events: none;
    line-height: 1;
}
.theme-toggle::before {
    content: "\263D";
    left: 8px;
}
.theme-toggle::after {
    content: "\2600";
    right: 8px;
}
.theme-toggle-thumb {
    position: absolute;
    top: 2px;
    left: 2px;
    width: 22px;
    height: 22px;
    background: var(--purple-neon);
    border-radius: 50%;
    transition: transform 0.25s cubic-bezier(0.4, 0, 0.2, 1), background-color 0.2s;
    box-shadow: 0 0 12px var(--purple-glow);
}
[data-theme="light"] .theme-toggle-thumb {
    transform: translateX(28px);
}

/* Cards */
.card {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 22px 24px;
    margin-bottom: 14px;
    transition: transform .25s ease, border-color .25s ease, box-shadow .25s ease, background 0.3s ease;
    position: relative;
    overflow: hidden;
    backdrop-filter: blur(14px);
    -webkit-backdrop-filter: blur(14px);
}
.card::before {
    content: '';
    position: absolute;
    inset: 0;
    background: radial-gradient(circle at 80% 0%, var(--purple-glow), transparent 50%);
    opacity: 0.10;
    pointer-events: none;
    transition: opacity .25s ease;
}
.card::after {
    content: '';
    position: absolute;
    left: 0; right: 0; bottom: 0;
    height: 2px;
    background: linear-gradient(90deg, transparent, var(--purple-neon), transparent);
    opacity: 0.4;
    transition: opacity .25s ease;
}
.card:hover {
    transform: translateY(-2px);
    border-color: var(--border-strong);
    box-shadow: var(--hover-shadow), 0 0 24px var(--purple-soft);
}
.card:hover::before { opacity: 0.22; }
.card:hover::after  { opacity: 1; }

.card h2 {
    font-size: 1.15rem;
    margin-bottom: 8px;
    color: var(--text-primary);
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
}

.card .meta {
    color: var(--text-muted);
    font-size: 0.85rem;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
}

.card p { color: var(--text-secondary); }

/* Badges */
.badge {
    display: inline-block;
    padding: 2px 10px;
    border-radius: 999px;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    border: 1px solid currentColor;
    background: var(--purple-soft);
}
.badge-beginner     { color: var(--purple-neon); }
.badge-intermediate { color: var(--warning); }
.badge-advanced     { color: #ff8b6b; }
[data-theme="light"] .badge-advanced { color: #c45a3a; }
.badge-completed {
    color: var(--success);
    border-color: var(--success);
    background: var(--result-success-bg);
    text-shadow: 0 0 4px var(--success-glow);
}
.badge-given-up {
    color: var(--danger);
    border-color: var(--danger);
    background: var(--result-failure-bg);
    text-shadow: 0 0 4px var(--danger-glow);
}

/* Category */
.category-header {
    display: flex;
    align-items: center;
    gap: 12px;
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--purple-text);
    margin: 28px 0 14px;
    padding: 0;
    border: none;
    text-transform: uppercase;
    letter-spacing: 0.18em;
    font-weight: 500;
}
.category-header::before {
    content: '';
    width: 8px; height: 8px;
    border-radius: 50%;
    background: var(--purple-neon);
    box-shadow: 0 0 10px var(--purple-glow);
    animation: pulse 2.4s ease-in-out infinite;
}
.category-header::after {
    content: '';
    flex: 1;
    height: 1px;
    background: linear-gradient(90deg, var(--border-strong), transparent);
}

/* Code editor (raw textarea fallback) */
.code-editor {
    width: 100%;
    min-height: 300px;
    background: var(--code-bg);
    color: #e6dcf2;
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 16px;
    font-family: var(--font-mono);
    font-size: 14px;
    line-height: 1.5;
    tab-size: 2;
    resize: vertical;
}
.code-editor:focus {
    outline: none;
    border-color: var(--purple-neon);
    box-shadow: 0 0 0 1px var(--purple-neon), 0 0 16px var(--purple-soft);
}

/* CodeMirror polish — editor stays dark in both themes for code legibility */
.CodeMirror {
    border-radius: 10px !important;
    box-shadow: 0 0 0 1px var(--border), 0 8px 24px rgba(0, 0, 0, 0.45);
    transition: box-shadow .2s ease;
}
.CodeMirror-focused {
    box-shadow: 0 0 0 1px var(--purple-neon), 0 0 22px var(--purple-soft) !important;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 9px 20px;
    border-radius: 8px;
    font-family: var(--font-ui);
    font-size: 0.9rem;
    font-weight: 500;
    letter-spacing: 0.02em;
    cursor: pointer;
    text-decoration: none;
    border: 1px solid var(--border);
    background: linear-gradient(180deg, var(--metal-2), var(--metal-1));
    color: var(--text-primary);
    box-shadow: var(--btn-shadow);
    transition: all .15s ease;
}
.btn:hover {
    border-color: var(--border-strong);
    color: var(--purple-neon);
    box-shadow: var(--btn-shadow), 0 0 18px var(--purple-soft);
}
.btn:active { transform: translateY(1px); }

.btn-primary {
    background: linear-gradient(180deg, var(--purple-neon), var(--purple-deep));
    color: #ffffff;
    border-color: var(--purple-neon);
    text-shadow: 0 0 6px rgba(0,0,0,0.30);
    box-shadow: var(--btn-primary-shadow);
    font-weight: 600;
}
.btn-primary:hover {
    color: #ffffff;
    box-shadow: var(--btn-primary-shadow), 0 0 28px var(--purple-glow);
}
[data-theme="dark"] .btn-primary { color: #150825; text-shadow: 0 0 6px rgba(255,255,255,0.30); }

.btn-secondary {
    background: linear-gradient(180deg, var(--metal-2), var(--metal-1));
    color: var(--text-secondary);
}
.btn-secondary:hover { color: var(--purple-neon); }

.btn-danger {
    background: linear-gradient(180deg, var(--danger), color-mix(in srgb, var(--danger) 60%, #4a0010));
    color: #ffffff;
    border-color: var(--danger);
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.25), 0 0 12px var(--danger-glow), 0 4px 12px rgba(0,0,0,0.4);
    font-weight: 600;
}
.btn-danger:hover {
    color: #ffffff;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.3), 0 0 22px var(--danger-glow), 0 4px 14px rgba(0,0,0,0.5);
}

.btn:disabled,
.btn-primary:disabled,
.btn-danger:disabled,
.btn-secondary:disabled {
    opacity: 0.45;
    cursor: not-allowed;
    box-shadow: none;
    transform: none;
}

.btn-group {
    display: flex;
    gap: 10px;
    margin-top: 20px;
    flex-wrap: wrap;
}

/* Result */
.result-box {
    border-radius: 12px;
    padding: 18px;
    margin-top: 20px;
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid var(--border);
    position: relative;
    overflow: hidden;
}
.result-box::before {
    content: '';
    position: absolute;
    inset: 0 0 auto 0;
    height: 1px;
    background: linear-gradient(90deg, transparent, currentColor, transparent);
    opacity: 0.7;
}
.result-success {
    background: var(--result-success-bg);
    border-color: var(--success);
    color: var(--success);
    box-shadow: 0 0 20px var(--success-glow);
}
.result-failure {
    background: var(--result-failure-bg);
    border-color: var(--danger);
    color: var(--danger);
    box-shadow: 0 0 20px var(--danger-glow);
}
.result-box h3 { margin-bottom: 8px; font-weight: 600; }
.result-success h3 { color: var(--success); text-shadow: 0 0 8px var(--success-glow); }
.result-failure h3 { color: var(--danger); text-shadow: 0 0 8px var(--danger-glow); }
.result-box pre {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    white-space: pre-wrap;
    color: var(--text-secondary);
    margin-top: 8px;
}

/* Concepts */
.concepts-section { margin-top: 32px; }
.concepts-section h2 {
    color: var(--purple-text);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    letter-spacing: 0.18em;
    text-transform: uppercase;
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 14px !important;
    font-weight: 500;
}
.concepts-section h2::before {
    content: '';
    width: 8px; height: 8px;
    border-radius: 50%;
    background: var(--purple-neon);
    box-shadow: 0 0 10px var(--purple-glow);
}
.concepts-section h2::after {
    content: '';
    flex: 1;
    height: 1px;
    background: linear-gradient(90deg, var(--border-strong), transparent);
}

.concept-card {
    background: var(--card-bg);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 18px 22px 18px 26px;
    margin-bottom: 14px;
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    position: relative;
    overflow: hidden;
}
.concept-card::before {
    content: '';
    position: absolute;
    left: 0; top: 0; bottom: 0;
    width: 3px;
    background: linear-gradient(180deg, var(--purple-neon), transparent);
    box-shadow: 0 0 12px var(--purple-glow);
}
.concept-card h3 {
    color: var(--purple-neon);
    font-size: 1rem;
    margin-bottom: 10px;
    text-shadow: 0 0 6px var(--purple-soft);
    font-weight: 600;
}
.concept-card p, .concept-text {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.65;
}
.concept-code {
    display: block;
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 12px 16px;
    margin: 10px 0;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    line-height: 1.5;
    overflow-x: auto;
    color: #d6cce8;
}
.concept-code code {
    font-family: inherit;
    background: none;
    padding: 0;
    border: none;
    color: inherit;
}
.concept-inline-code {
    background: var(--purple-soft);
    border: 1px solid var(--border);
    border-radius: 4px;
    padding: 1px 6px;
    font-family: var(--font-mono);
    font-size: 0.85em;
    color: #7ee787;
}
[data-theme="light"] .concept-inline-code { color: #1a7d40; }

/* Progress */
.progress-bar {
    display: flex;
    align-items: center;
    gap: 14px;
    margin-bottom: 24px;
    color: var(--text-secondary);
    font-size: 0.85rem;
    font-family: var(--font-mono);
    padding: 12px 18px;
    background: var(--bg-elevated);
    border: 1px solid var(--border);
    border-radius: 12px;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    flex-wrap: wrap;
}
.progress-counter-solved  { color: var(--success); font-weight: 600; text-shadow: 0 0 6px var(--success-glow); }
.progress-counter-givenup { color: var(--danger);  font-weight: 600; text-shadow: 0 0 6px var(--danger-glow); }

.progress-fill {
    flex: 1;
    height: 6px;
    background: var(--purple-soft);
    border-radius: 3px;
    overflow: hidden;
    display: flex;
    min-width: 160px;
}
.progress-fill-inner {
    height: 100%;
    background: linear-gradient(90deg, var(--success), color-mix(in srgb, var(--success) 70%, var(--purple-neon)));
    transition: width 0.4s ease;
    box-shadow: 0 0 10px var(--success-glow);
}
.progress-fill-givenup {
    height: 100%;
    background: var(--danger);
    transition: width 0.4s ease;
    box-shadow: 0 0 10px var(--danger-glow);
}

/* Challenge description */
.challenge-description {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-left: 3px solid var(--purple-neon);
    box-shadow: -10px 0 20px -10px var(--purple-soft);
    padding: 16px 20px;
    margin-bottom: 22px;
    border-radius: 0 12px 12px 0;
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    color: var(--text-primary);
}

/* Breadcrumb */
.breadcrumb {
    margin-bottom: 22px;
    font-size: 0.78rem;
    font-family: var(--font-mono);
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--text-muted);
}
.breadcrumb-link {
    color: var(--purple-text);
    text-decoration: none;
    cursor: pointer;
    background: none;
    border: none;
    font-size: inherit;
    font-family: inherit;
    letter-spacing: inherit;
    text-transform: inherit;
    padding: 0;
    transition: color .15s ease, text-shadow .15s ease;
}
.breadcrumb-link:hover {
    color: var(--purple-neon);
    text-shadow: 0 0 6px var(--purple-glow);
}
.breadcrumb-sep { color: var(--text-muted); margin: 0 10px; opacity: 0.6; }
.breadcrumb-current { color: var(--text-primary); font-weight: 500; }
.breadcrumb-counter { color: var(--text-muted); margin-left: 10px; font-size: 0.75rem; }

a.challenge-link { color: var(--text-primary); text-decoration: none; display: block; }

/* ============================
   Give Up feature
   ============================ */

/* Hidden snapshot of the original buggy code */
.buggy-snapshot {
    position: absolute;
    left: -9999px;
    width: 1px;
    height: 1px;
    opacity: 0;
    pointer-events: none;
}

/* Flip card: editor on the front, solution diff on the back */
.giveup-flip {
    perspective: 1400px;
    margin-bottom: 14px;
}
.giveup-flip-inner {
    position: relative;
    display: grid;
    grid-template-areas: "stack";
    transform-style: preserve-3d;
    transition: transform 0.9s cubic-bezier(0.3, 0.1, 0.2, 1);
}
.giveup-flip.flipped .giveup-flip-inner {
    transform: rotateY(180deg);
}
.giveup-flip.no-animate .giveup-flip-inner {
    transition: none;
}
.giveup-flip-face {
    grid-area: stack;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
}
.giveup-flip-back {
    transform: rotateY(180deg);
}
.challenge-flip .giveup-flip-front,
.challenge-flip .giveup-flip-back {
    min-height: 120px;
}

/* "SOLUTION REVEALED" header above the diff */
.solution-label {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 8px;
}
.solution-label-badge {
    background: linear-gradient(180deg, var(--danger), color-mix(in srgb, var(--danger) 60%, #2a0008));
    color: #ffffff;
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 700;
    letter-spacing: 0.16em;
    padding: 4px 10px;
    border-radius: 4px;
    box-shadow: 0 0 12px var(--danger-glow);
    border: 1px solid var(--danger);
}
.solution-label-text {
    color: var(--text-secondary);
    font-size: 0.88rem;
}

/* Diff block — kept dark and IDE-like in both themes */
.mock-code {
    background: #150e25;
    color: #d6cce8;
    padding: 14px 16px;
    border-radius: 10px;
    font-family: var(--font-mono);
    font-size: 0.88rem;
    line-height: 1.55;
    border: 1px solid var(--border);
    margin: 10px 0 12px;
    white-space: pre;
    overflow-x: auto;
    box-shadow: 0 0 0 1px var(--border), 0 8px 24px rgba(0, 0, 0, 0.4);
}
.mock-code .kw  { color: #c084fc; font-weight: 600; }
.mock-code .str { color: #ffb86c; }
.mock-code .num { color: #b5cea8; }
.mock-code .cm  { color: #6a9955; font-style: italic; }

.mock-code-diff { line-height: 1.6; }
.mock-code-diff .dim { display: block; opacity: 0.55; }
.mock-code-diff .line-rem {
    display: block;
    background: color-mix(in srgb, var(--diff-rem) 22%, transparent);
    color: #ffb4b4;
    border-left: 3px solid var(--diff-rem);
    padding-left: 6px;
    margin-left: -9px;
}
.mock-code-diff .line-add {
    display: block;
    background: color-mix(in srgb, var(--diff-add) 22%, transparent);
    color: #b6f2c1;
    border-left: 3px solid var(--diff-add);
    padding-left: 6px;
    margin-left: -9px;
}

.solution-diff { margin-bottom: 14px; }
.solution-diff .line-add { animation: diffAddPulse 0.6s 0.2s 2 both; }
.solution-diff .line-rem { animation: diffRemPulse 0.6s 0.2s 2 both; }

@keyframes diffAddPulse {
    0%   { background: color-mix(in srgb, var(--diff-add) 22%, transparent); }
    50%  { background: color-mix(in srgb, var(--diff-add) 55%, transparent); }
    100% { background: color-mix(in srgb, var(--diff-add) 22%, transparent); }
}
@keyframes diffRemPulse {
    0%   { background: color-mix(in srgb, var(--diff-rem) 22%, transparent); }
    50%  { background: color-mix(in srgb, var(--diff-rem) 55%, transparent); }
    100% { background: color-mix(in srgb, var(--diff-rem) 22%, transparent); }
}

/* ============================
   Sidebar / Challenge Tree
   ============================ */

.app-layout {
    display: flex;
    min-height: 100vh;
    align-items: stretch;
}
.app-main {
    flex: 1;
    min-width: 0;
}

.sidebar {
    width: 280px;
    flex-shrink: 0;
    background: var(--sidebar-bg);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    transition: width 0.2s ease, background-color 0.2s;
    overflow: hidden;
    backdrop-filter: blur(14px);
    -webkit-backdrop-filter: blur(14px);
    position: sticky;
    top: 0;
    height: 100vh;
    z-index: 90;
}
.sidebar.collapsed { width: 44px; }

.sidebar-header {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 0 12px;
    border-bottom: 1px solid var(--border);
    background: var(--sidebar-header-bg);
    height: var(--ide-tabbar-height, 40px);
    min-height: var(--ide-tabbar-height, 40px);
    box-sizing: border-box;
    flex-shrink: 0;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
}
.sidebar-toggle {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 4px;
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all .15s ease;
}
.sidebar-toggle:hover {
    background: var(--hover-bg-strong);
    color: var(--purple-neon);
    box-shadow: 0 0 10px var(--purple-soft);
}
.sidebar-title {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.18em;
    color: var(--purple-text);
    text-transform: uppercase;
    white-space: nowrap;
    opacity: 1;
    transition: opacity 0.15s;
}
.sidebar.collapsed .sidebar-title,
.sidebar.collapsed .sidebar-tree {
    opacity: 0;
    pointer-events: none;
}

.sidebar-tree {
    flex: 1;
    overflow-y: auto;
    padding: 10px 0;
    font-size: 0.85rem;
}

.tree-category { margin-bottom: 4px; }
.tree-category-header {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 6px 12px;
    cursor: pointer;
    color: var(--text-primary);
    user-select: none;
    white-space: nowrap;
    font-family: var(--font-mono);
    font-size: 0.74rem;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    transition: background-color .12s;
}
.tree-category-header:hover { background: var(--hover-bg); }

.tree-chevron {
    display: inline-block;
    color: var(--text-muted);
    font-size: 0.7rem;
    width: 10px;
    transition: transform 0.2s ease;
    transform: rotate(-90deg);
}
.tree-category.expanded .tree-chevron {
    transform: rotate(0deg);
    color: var(--purple-neon);
}
.tree-category-name { font-size: 0.74rem; }

.tree-category-children { display: none; padding-left: 6px; }
.tree-category.expanded .tree-category-children { display: block; }

.tree-challenge {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 5px 12px 5px 28px;
    color: var(--text-secondary);
    text-decoration: none;
    cursor: pointer;
    border: none;
    background: none;
    font-family: inherit;
    font-size: 0.82rem;
    width: 100%;
    text-align: left;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    transition: background-color .12s, color .12s, padding-left .12s;
}
.tree-challenge:hover {
    background: var(--hover-bg);
    color: var(--text-primary);
}
.tree-challenge-active {
    background: var(--accent-bg);
    color: var(--text-primary);
    border-left: 2px solid var(--purple-neon);
    padding-left: 26px;
    box-shadow: inset 6px 0 16px var(--purple-soft);
    text-shadow: 0 0 6px var(--purple-soft);
}
.tree-challenge-active:hover {
    background: var(--accent-bg);
    filter: brightness(1.12);
}

.tree-file-icon {
    color: var(--purple-neon);
    font-size: 0.78rem;
    flex-shrink: 0;
    opacity: 0.65;
}
.tree-challenge-active .tree-file-icon { opacity: 1; }
.tree-challenge-title {
    overflow: hidden;
    text-overflow: ellipsis;
    flex: 1;
}
.tree-check {
    color: var(--success);
    font-size: 0.85rem;
    flex-shrink: 0;
    text-shadow: 0 0 6px var(--success-glow);
}
.tree-cross {
    color: var(--danger);
    font-size: 0.95rem;
    font-weight: 700;
    flex-shrink: 0;
    text-shadow: 0 0 6px var(--danger-glow);
}

@media (max-width: 768px) {
    .sidebar { width: 44px; }
    .sidebar:not(.collapsed) {
        position: fixed;
        z-index: 200;
        height: 100vh;
        width: 260px;
        box-shadow: 4px 0 14px rgba(0, 0, 0, 0.4);
    }
}

/* Scrollbar */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: var(--bg-base); }
::-webkit-scrollbar-thumb {
    background: linear-gradient(180deg, var(--metal-2), var(--metal-1));
    border-radius: 8px;
    border: 2px solid var(--bg-base);
}
::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(180deg, var(--purple-deep), var(--metal-2));
}

/* ============================================================
   GitHub auth — Sign-in button, chip, sync dot, disclosure modal
   ============================================================ */

.github-signin {
    display: inline-flex;
    align-items: center;
    gap: 7px;
    padding: 6px 12px;
    border-radius: 8px;
    background: linear-gradient(180deg, var(--metal-2), var(--metal-1));
    border: 1px solid var(--border);
    color: var(--text-primary);
    text-decoration: none;
    font-size: 0.85rem;
    font-weight: 500;
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.06), 0 2px 6px rgba(0,0,0,0.30);
    transition: all .15s ease;
}
.github-signin:hover {
    border-color: var(--border-strong);
    color: var(--purple-neon);
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.08), 0 0 16px var(--purple-soft);
}
.github-signin svg { flex-shrink: 0; }

.github-chip {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 4px 6px 4px 4px;
    border-radius: 999px;
    background: linear-gradient(135deg, var(--metal-1), var(--metal-2) 60%, var(--metal-1));
    border: 1px solid var(--border);
    box-shadow: inset 0 1px 0 rgba(255,255,255,0.06), 0 2px 8px rgba(0,0,0,0.30);
}
.gh-avatar-wrap {
    position: relative;
    display: inline-flex;
    align-items: center;
    flex-shrink: 0;
}
.github-chip .gh-avatar {
    width: 24px; height: 24px;
    border-radius: 50%;
    border: 1px solid var(--purple-neon);
    box-shadow: 0 0 6px var(--purple-soft);
    display: block;
}
.gh-sync-dot {
    position: absolute;
    right: -2px; bottom: -2px;
    width: 10px; height: 10px;
    border-radius: 50%;
    border: 2px solid var(--bg-base);
    background: var(--text-secondary);
    transition: background-color .15s ease, box-shadow .15s ease;
    box-sizing: border-box;
}
.gh-sync-idle    { background: var(--text-secondary); }
.gh-sync-syncing { background: var(--warning); animation: ghSyncPulse 1.1s ease-in-out infinite; }
.gh-sync-success { background: var(--success); box-shadow: 0 0 6px var(--success-glow); }
.gh-sync-error   { background: var(--danger);  box-shadow: 0 0 6px var(--danger-glow); }
@keyframes ghSyncPulse {
    0%, 100% { transform: scale(1);   opacity: 1; }
    50%      { transform: scale(1.3); opacity: 0.7; }
}

.github-chip .gh-login {
    color: var(--text-primary);
    font-size: 0.82rem;
    font-weight: 500;
    max-width: 130px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
.github-chip .gh-action {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 22px; height: 22px;
    border-radius: 50%;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.85rem;
    border: 1px solid transparent;
    transition: all .15s ease;
}
.github-chip .gh-action:hover {
    color: var(--purple-neon);
    background: var(--purple-soft);
    border-color: var(--border-strong);
}

/* Disclosure modal */
.signin-modal {
    position: fixed;
    inset: 0;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(8, 5, 18, 0.65);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    padding: 20px;
}
.signin-modal[hidden] { display: none; }
.signin-modal-box {
    background: var(--card-bg);
    border: 1px solid var(--border-strong);
    border-radius: 16px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.6), 0 0 32px var(--purple-soft);
    padding: 26px 28px 22px;
    max-width: 520px;
    width: 100%;
    color: var(--text-primary);
    backdrop-filter: blur(14px);
}
.signin-modal-title {
    margin: 0 0 14px;
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--purple-neon);
    text-shadow: 0 0 8px var(--purple-soft);
}
.signin-modal-body { font-size: 0.92rem; line-height: 1.55; color: var(--text-secondary); }
.signin-modal-body p { margin: 0 0 10px; }
.signin-modal-body code {
    font-family: var(--font-mono);
    font-size: 0.85em;
    background: var(--purple-soft);
    border: 1px solid var(--border);
    padding: 1px 6px;
    border-radius: 4px;
    color: var(--purple-text);
}
.signin-modal-actions {
    display: flex;
    gap: 10px;
    justify-content: flex-end;
    margin-top: 18px;
}

/* ============================================================
   Snake Training — yellow accent palette overrides
   Recasts the purple base to a warm Nokia-screen yellow.
   ============================================================ */

[data-theme="dark"] {
    --purple-neon:       #ffe066;
    --purple-glow:       rgba(255, 224, 102, 0.55);
    --purple-soft:       rgba(255, 224, 102, 0.18);
    --purple-deep:       #b58800;
    --purple-text:       #ffe98a;
    --accent:            #ffe066;
    --accent-hover:      #fff2a8;
    --accent-bg:         rgba(255, 224, 102, 0.14);
    --border:            rgba(255, 224, 102, 0.16);
    --border-strong:     rgba(255, 224, 102, 0.36);
    --hover-bg:          rgba(255, 224, 102, 0.07);
    --hover-bg-strong:   rgba(255, 224, 102, 0.14);
    --title-gradient:    linear-gradient(135deg, #ffffff 0%, #ffe98a 50%, #ffe066 100%);
    --shadow-glow:       0 0 32px rgba(255, 224, 102, 0.20);
    --btn-primary-shadow:
        inset 0 1px 0 rgba(255,255,255,0.4),
        0 0 18px rgba(255, 224, 102, 0.55),
        0 6px 18px rgba(0,0,0,0.4);
    --backdrop:
        radial-gradient(ellipse 70% 50% at 30% 0%, rgba(255, 224, 102, 0.12), transparent 60%),
        radial-gradient(ellipse 50% 40% at 80% 100%, rgba(255, 224, 102, 0.05), transparent 65%),
        linear-gradient(180deg, #14110a 0%, #0e0c08 60%, #0b0906 100%);
    --bg-base:           #0b0906;
    --bg-deep:           #0e0c08;
    --bg-primary:        #0b0906;
    --bg-secondary:      #14110a;
    --bg-card:           rgba(38, 32, 18, 0.74);
    --code-bg:           #0a0805;
}

[data-theme="light"] {
    --purple-neon:       #f9a825;
    --purple-glow:       rgba(249, 168, 37, 0.45);
    --purple-soft:       rgba(249, 168, 37, 0.16);
    --purple-deep:       #6d4c00;
    --purple-text:       #b58800;
    --accent:            #f9a825;
    --accent-hover:      #f57f17;
    --accent-bg:         rgba(249, 168, 37, 0.14);
    --border:            rgba(249, 168, 37, 0.22);
    --border-strong:     rgba(249, 168, 37, 0.45);
    --hover-bg:          rgba(249, 168, 37, 0.07);
    --hover-bg-strong:   rgba(249, 168, 37, 0.16);
    --title-gradient:    linear-gradient(135deg, #f57f17 0%, #f9a825 50%, #fbc02d 100%);
    --shadow-glow:       0 0 32px rgba(249, 168, 37, 0.18);
    --btn-primary-shadow:
        inset 0 1px 0 rgba(255,255,255,0.5),
        0 0 14px rgba(249, 168, 37, 0.45),
        0 4px 12px rgba(0,0,0,0.12);

    /* Light backgrounds for the IDE-specific surfaces; the original light
       theme kept code-bg dark which is unreadable for inline code here. */
    --code-bg:           #fff8e1;
    --bg-base:           #fffdf5;
    --bg-deep:           #fbf5e0;
    --bg-primary:        #fffdf5;
    --bg-secondary:      #fdf6dc;
    --bg-card:           #ffffff;
    --sidebar-bg:        #fdf6dc;
    --sidebar-header-bg: #f8eec0;
    --header-bg:         #ffffff;
    --backdrop:          linear-gradient(180deg, #ffffff 0%, #fdf6dc 100%);
}

/* ============================================================
   Training IDE layout — 3 zones (left tree, center editor + terminal,
   right preview/lesson). Sits on top of the standard app-layout.
   ============================================================ */

:root {
    --ide-tabbar-height: 40px;
}

.ide-shell {
    display: flex;
    flex-direction: column;
    flex: 1;
    min-width: 0;
    min-height: 0;
    border-top: 1px solid var(--border);
}

.ide-center {
    display: flex;
    flex-direction: column;
    flex: 1;
    min-width: 0;
    min-height: 0;
    position: relative;            /* containing block for the terminal overlay */
}

.ide-side {
    display: flex;
    flex-direction: column;
    min-width: 0;
    background: var(--bg-secondary);
}

.editor-tabs {
    display: flex;
    align-items: stretch;
    gap: 2px;
    background: var(--bg-secondary);
    padding: 0 6px;
    height: var(--ide-tabbar-height);
    min-height: var(--ide-tabbar-height);
    box-sizing: border-box;
    flex-shrink: 0;
    overflow-x: auto;
}

.editor-tab {
    display: inline-flex;
    align-items: center;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: 0 14px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    cursor: pointer;
    white-space: nowrap;
    box-shadow: inset 0 -2px 0 transparent;
}

.editor-tab:hover {
    color: var(--text-primary);
    background: var(--hover-bg);
}

.editor-tab.active {
    color: var(--text-primary);
    background: var(--bg-base);
    box-shadow: inset 0 -2px 0 var(--accent);
}

.editor-tab.preview-tab {
    margin-left: auto;
    color: var(--accent);
}

.editor-tab.preview-tab.active {
    color: var(--accent-hover);
}

/* Submit tab — the IDE-side counterpart of the lesson "Next" button. */
.submit-tab {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    align-self: center;
    background: var(--accent);
    color: #1a1a1a;
    border: 1px solid var(--accent);
    padding: 0 12px;
    height: 28px;
    margin-left: 6px;
    font-family: var(--font-ui);
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
    border-radius: 4px;
    flex-shrink: 0;
}

.submit-tab:hover:not([disabled]) {
    background: var(--accent-hover);
    border-color: var(--accent-hover);
}

.submit-tab[disabled] {
    opacity: 0.4;
    cursor: not-allowed;
}

.editor-tab-icon {
    margin-right: 6px;
    opacity: 0.7;
}

.editor-pane {
    flex: 1 1 auto;
    min-height: 0;
    overflow: hidden;
    background: var(--bg-base);
    position: relative;
}

.editor-pane > .preview-frame,
.editor-pane > #cmEditor {
    position: absolute;
    inset: 0;
}

.editor-pane.show-preview > #cmEditor { display: none; }
.editor-pane.show-editor  > .preview-frame { display: none; }

.editor-pane .CodeMirror {
    height: 100%;
    border: none !important;
    border-radius: 0 !important;
    font-size: 14px;
    font-family: var(--font-mono);
}

.editor-pane .CodeMirror-matchingbracket {
    background: rgba(255, 200, 0, 0.35) !important;
    color: inherit !important;
    border-radius: 2px;
    box-shadow: 0 0 6px rgba(255, 200, 0, 0.55);
}
.editor-pane .CodeMirror-nonmatchingbracket {
    background: rgba(220, 50, 50, 0.3) !important;
    color: inherit !important;
    border-radius: 2px;
}

/* Sidebar footer holds the IDE tool buttons (Terminal, etc.) IntelliJ-style. */
.sidebar-footer {
    margin-top: auto;
    padding: 4px;
    border-top: 1px solid var(--border);
    background: var(--sidebar-header-bg);
    flex-shrink: 0;
}

.sidebar-tool-btn {
    display: flex;
    align-items: center;
    gap: 10px;
    width: 100%;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: 6px 8px;
    cursor: pointer;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.18em;
    text-transform: uppercase;
    border-radius: 6px;
    text-align: left;
}

.sidebar-tool-btn:hover {
    background: var(--hover-bg-strong);
    color: var(--purple-text);
}

.sidebar-tool-btn.active {
    background: var(--accent-bg);
    color: var(--accent);
}

.sidebar-tool-icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 22px;
    height: 22px;
    flex-shrink: 0;
}

.sidebar.collapsed .sidebar-tool-label {
    display: none;
}

/* Terminal as a slide-up overlay over the editor pane (IntelliJ-style). */
.terminal-overlay {
    position: absolute;
    left: 0;
    right: 0;
    bottom: 0;
    height: 45%;
    min-height: 180px;
    background: var(--bg-base);
    border-top: 1px solid var(--border);
    box-shadow: 0 -6px 16px rgba(0, 0, 0, 0.22);
    transform: translateY(100%);
    transition: transform 0.22s ease-out;
    z-index: 8;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.terminal-overlay.open {
    transform: translateY(0);
}

.terminal-overlay-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 6px 12px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    flex-shrink: 0;
}

.terminal-overlay-title {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.14em;
    color: var(--text-muted);
}

.terminal-close {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    width: 24px;
    height: 24px;
    border-radius: 4px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
}

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

.terminal-overlay-body {
    flex: 1;
    padding: 12px 14px;
    overflow-y: auto;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.side-tabs {
    display: flex;
    align-items: center;
    border-bottom: 1px solid var(--border);
    background: var(--bg-secondary);
    flex-shrink: 0;
    padding-right: 6px;
}

.side-tab {
    background: transparent;
    border: none;
    border-bottom: 2px solid transparent;
    color: var(--text-secondary);
    padding: 10px 18px;
    font-family: var(--font-ui);
    font-size: 0.85rem;
    cursor: pointer;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.side-tab.active {
    color: var(--text-primary);
    border-bottom-color: var(--accent);
}

.panel-collapse-btn {
    margin-left: auto;
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-secondary);
    width: 26px;
    height: 26px;
    border-radius: 4px;
    cursor: pointer;
    line-height: 1;
    font-size: 0.95rem;
}

.panel-collapse-btn:hover {
    color: var(--text-primary);
    border-color: var(--accent);
}

.ide-shell.lesson-collapsed .ide-side .side-tab,
.ide-shell.lesson-collapsed .ide-side .side-content {
    display: none;
}

.ide-side-collapsed-strip {
    display: none;
    flex-direction: column;
    align-items: center;
    padding: 16px 0;
    cursor: pointer;
    color: var(--text-secondary);
    user-select: none;
}

.ide-shell.lesson-collapsed .ide-side-collapsed-strip {
    display: flex;
}

.ide-side-collapsed-strip .strip-label {
    writing-mode: vertical-rl;
    transform: rotate(180deg);
    text-transform: uppercase;
    letter-spacing: 0.12em;
    font-size: 0.75rem;
    margin-top: 12px;
}

.ide-side-collapsed-strip:hover {
    color: var(--accent);
}

.side-content {
    flex: 1 1 auto;
    min-height: 0;
    overflow: hidden;
    background: var(--bg-base);
}

.preview-frame {
    width: 100%;
    height: 100%;
    border: none;
    background: white;
}

.lesson-content {
    height: 100%;
    overflow-y: auto;
    padding: 24px 28px;
    color: var(--text-primary);
    line-height: 1.65;
}

.lesson-content h1, .lesson-content h2, .lesson-content h3 {
    color: var(--text-primary);
    margin-top: 0;
}

.lesson-content code {
    font-family: var(--font-mono);
    font-size: 0.88em;
    background: var(--code-bg);
    padding: 2px 6px;
    border-radius: 4px;
}

.lesson-content ol, .lesson-content ul {
    padding-left: 22px;
}

.lesson-content li {
    margin-bottom: 6px;
}

.lesson-goal {
    background: var(--accent-bg);
    border-left: 3px solid var(--accent);
    padding: 12px 16px;
    margin: 0 0 20px;
    border-radius: 0 6px 6px 0;
}

.lesson-goal strong {
    color: var(--accent-hover);
    text-transform: uppercase;
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    display: block;
    margin-bottom: 4px;
}

.lesson-actions {
    display: flex;
    gap: 10px;
    margin-top: 24px;
    padding-top: 18px;
    border-top: 1px solid var(--border);
    flex-wrap: wrap;
}

.lesson-hint {
    margin-top: 20px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 14px 16px;
}

.lesson-hint summary {
    cursor: pointer;
    color: var(--text-secondary);
    user-select: none;
}

/* ============================================================
   Lesson / Code flip
   ============================================================ */

.app-main {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Base CSS gives the header a 30px bottom margin (for the cert layouts).
   The training page has the stepper sitting flush below the header, so
   that margin shows up as a blank strip. Zero it out here. */
.app-main > .header {
    margin-bottom: 0;
}

.lesson-flip {
    flex: 1;
    min-height: 0;
    perspective: 1400px;
}

.lesson-flip-inner {
    position: relative;
    display: grid;
    grid-template-areas: "stack";
    height: 100%;
    transform-style: preserve-3d;
    transition: transform 0.9s cubic-bezier(0.3, 0.1, 0.2, 1);
}

.lesson-flip.flipped .lesson-flip-inner {
    transform: rotateY(180deg);
}

.lesson-flip-face {
    grid-area: stack;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    height: 100%;
    overflow: hidden;
}

.lesson-flip-back {
    transform: rotateY(180deg);
}

/* The hidden face still occupies the same grid cell, so it would
   intercept clicks. Disable pointer-events on whichever face is not
   currently showing. */
.lesson-flip:not(.flipped) .lesson-flip-back { pointer-events: none; }
.lesson-flip.flipped         .lesson-flip-front { pointer-events: none; }

.lesson-flip-back .app-layout {
    min-height: 0;
    height: 100%;
}

/* Full-width lesson reading view */
.lesson-full {
    height: 100%;
    overflow-y: auto;
    background: var(--bg-base);
}

.lesson-full-inner {
    max-width: 780px;
    margin: 0 auto;
    padding: 40px 32px 80px;
    color: var(--text-primary);
}

.lesson-full-inner h2.lesson-title {
    margin: 0 0 8px;
    font-size: 1.6rem;
    background: var(--title-gradient);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}

.lesson-full-inner .lesson-subline {
    color: var(--text-secondary);
    font-size: 0.85rem;
    margin-bottom: 24px;
}

.lesson-full .lesson-content {
    padding: 0;
    height: auto;
    overflow: visible;
}

.lesson-full .lesson-actions {
    margin-top: 36px;
    border-top: none;
    padding-top: 0;
}

/* Icon button at the left of the file tab strip — returns from Code → Lesson */
.back-to-lesson-tab {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    align-self: center;
    background: transparent;
    border: 1px solid transparent;
    color: var(--text-secondary);
    width: 32px;
    height: 28px;
    padding: 0;
    margin-right: 6px;
    border-radius: 6px;
    cursor: pointer;
    flex-shrink: 0;
}

.back-to-lesson-tab:hover {
    color: var(--accent);
    background: var(--hover-bg);
}

.back-to-lesson-tab:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 1px;
}

/* Stepper across the top */
.lesson-stepper {
    display: flex;
    align-items: center;
    gap: 4px;
    padding: 12px 20px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    overflow-x: auto;
}

.stepper-item {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-secondary);
    width: 30px;
    height: 30px;
    border-radius: 50%;
    font-size: 0.78rem;
    font-family: var(--font-mono);
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.stepper-item:hover {
    color: var(--text-primary);
    border-color: var(--accent);
}

.stepper-item.active {
    background: var(--accent);
    color: var(--bg-base);
    border-color: var(--accent);
    box-shadow: 0 0 12px var(--purple-glow);
}

.stepper-line {
    width: 16px;
    height: 1px;
    background: var(--border);
    flex-shrink: 0;
}

.stepper-label {
    margin-left: 14px;
    color: var(--text-secondary);
    font-size: 0.85rem;
}

.stepper-label strong {
    color: var(--text-primary);
}

/* File tree (reuses .sidebar from existing CSS but lighter) */
.training-tree-file {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 6px 14px 6px 22px;
    color: var(--text-secondary);
    cursor: pointer;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    background: transparent;
    border: none;
    width: 100%;
    text-align: left;
}

.training-tree-file:hover {
    background: var(--hover-bg);
    color: var(--text-primary);
}

.training-tree-file.active {
    background: var(--accent-bg);
    color: var(--text-primary);
}

.training-tree-file-icon {
    opacity: 0.6;
}