:root {
            --bg-color: #060c14;
            --container-bg: #0a1420;
            --card-bg: #0f1c2c;
            --border-color: #1e3348;
            --text-primary: #e6f1ff;
            --text-secondary: #7c93ab;
            --accent-teal: #22d3ee;
            --accent-green: #34d399;
            --accent-red: #f87171;
            --accent-amber: #fbbf24;
            --font-display: 'Sora', sans-serif;
            --font-mono: 'JetBrains Mono', monospace;
            --shadow-color: rgba(0, 0, 0, 0.6);
            --panel-sunken: rgba(0, 0, 0, 0.35);

            /* Shared kit mapping */
            --kit-accent: var(--accent-teal);
            --kit-accent-ink: #00232b;
            --kit-accent-glow: rgba(34, 211, 238, 0.25);
            --kit-surface: var(--card-bg);
            --kit-border: var(--border-color);
            --kit-input-bg: var(--container-bg);
            --kit-error: var(--accent-red);
        }

        /* TRUE LIGHT THEME — bright dashboard-white lab console, not a
           second dark palette. Backgrounds sit in the #f5f7fb–#ffffff
           range with dark, readable text throughout. */
        body.light-mode {
            --bg-color: #f2f5fa;
            --container-bg: #ffffff;
            --card-bg: #f7f9fc;
            --border-color: #cbd8e6;
            --text-primary: #0b1c2c;
            --text-secondary: #4b6478;
            --accent-teal: #0891b2;
            --accent-green: #15803d;
            --accent-red: #dc2626;
            --accent-amber: #b45309;
            --shadow-color: rgba(15, 40, 60, 0.12);
            --panel-sunken: rgba(11, 28, 44, 0.05);

            /* Shared kit mapping (light) — redeclared in full: a custom
               property whose value is var(--other-var) does not reliably
               re-track that other var's light-mode override, so every
               --kit-* token must be restated here, not just the ink. */
            --kit-accent: var(--accent-teal);
            --kit-accent-ink: #000000;
            --kit-accent-glow: rgba(8, 145, 178, 0.18);
            --kit-surface: var(--card-bg);
            --kit-border: var(--border-color);
            --kit-input-bg: var(--container-bg);
            --kit-error: var(--accent-red);
        }

        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            transition: background-color 0.25s ease, color 0.25s ease, border-color 0.25s ease;
        }

        body {
            background-color: var(--bg-color);
            color: var(--text-primary);
            font-family: var(--font-mono);
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        .top-controls {
            position: fixed;
            top: 20px;
            right: 24px;
            z-index: 1000;
        }

        .theme-toggle-btn {
            background: var(--container-bg);
            color: var(--text-primary);
            border: 2px solid var(--border-color);
            padding: 8px 16px;
            border-radius: 8px;
            font-family: var(--font-mono);
            font-weight: 700;
            font-size: 0.85rem;
            cursor: pointer;
            box-shadow: 0 4px 10px var(--shadow-color);
            display: flex;
            align-items: center;
            gap: 6px;
        }

        .theme-toggle-btn:hover {
            border-color: var(--accent-teal);
            color: var(--accent-teal);
        }

        .dash-container {
            width: 100%;
            max-width: 860px;
            background: var(--container-bg);
            border: 2px solid var(--border-color);
            border-top: 6px solid var(--accent-teal);
            border-radius: 12px;
            padding: 36px;
            box-shadow: 0 16px 40px var(--shadow-color);
            min-height: 580px;
            display: flex;
            flex-direction: column;
            justify-content: space-between;
        }

        .dash-title {
            font-family: var(--font-display);
            font-size: 2rem;
            font-weight: 800;
            color: var(--accent-teal);
            text-align: center;
            letter-spacing: 0.5px;
            margin-bottom: 6px;
        }

        .dash-subtitle {
            font-family: var(--font-mono);
            text-align: center;
            color: var(--text-secondary);
            font-size: 0.9rem;
            margin-bottom: 22px;
            letter-spacing: 0.5px;
            text-transform: uppercase;
        }

        .status-bar {
            display: flex;
            justify-content: space-between;
            align-items: center;
            background: var(--panel-sunken);
            border: 1px solid var(--border-color);
            padding: 12px 20px;
            margin-bottom: 20px;
            border-radius: 8px;
            font-family: var(--font-mono);
            flex-wrap: wrap;
            gap: 8px;
        }

        .status-item {
            display: flex;
            align-items: center;
            gap: 8px;
            font-size: 0.9rem;
            font-weight: 700;
        }

        .status-label {
            color: var(--text-secondary);
        }

        .status-value {
            color: var(--accent-teal);
            font-size: 1rem;
        }

        /* Function Input/Output Mapping Diagram */
        .mapping-diagram {
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 16px;
            background: var(--panel-sunken);
            border: 1px dashed var(--accent-teal);
            border-radius: 8px;
            padding: 14px;
            margin-bottom: 18px;
        }

        .map-node {
            display: flex;
            flex-direction: column;
            align-items: center;
            min-width: 90px;
        }

        .map-label {
            font-size: 0.68rem;
            color: var(--text-secondary);
            letter-spacing: 1px;
            margin-bottom: 4px;
        }

        .map-value {
            font-family: var(--font-display);
            font-size: 1.4rem;
            font-weight: 700;
            color: var(--accent-green);
        }

        .map-arrow {
            font-family: var(--font-mono);
            color: var(--accent-teal);
            font-weight: 700;
            font-size: 0.95rem;
        }

        .telemetry-card {
            background: var(--card-bg);
            border: 1px solid var(--border-color);
            border-left: 4px solid var(--accent-teal);
            padding: 22px;
            margin-bottom: 22px;
            border-radius: 6px;
        }

        .telemetry-tag {
            font-family: var(--font-mono);
            font-size: 0.72rem;
            text-transform: uppercase;
            color: var(--accent-teal);
            font-weight: 700;
            margin-bottom: 10px;
            letter-spacing: 1px;
        }

        .telemetry-text {
            font-family: var(--font-display);
            font-size: 1.12rem;
            line-height: 1.6;
            font-weight: 600;
        }

        .options-grid {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 14px;
            margin-bottom: 16px;
        }

        @media (max-width: 640px) {
            .options-grid { grid-template-columns: 1fr; }
        }

        .option-btn {
            background: var(--card-bg);
            color: var(--text-primary);
            border: 1px solid var(--border-color);
            padding: 16px;
            border-radius: 8px;
            font-family: var(--font-mono);
            font-size: 1rem;
            font-weight: 600;
            text-align: left;
            cursor: pointer;
            display: flex;
            align-items: center;
            gap: 12px;
        }

        .option-btn:hover {
            border-color: var(--accent-teal);
            background: var(--panel-sunken);
        }

        .option-key {
            font-family: var(--font-mono);
            background: var(--border-color);
            color: var(--text-primary);
            width: 28px;
            height: 28px;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 0.85rem;
            font-weight: 700;
            border-radius: 6px;
            flex-shrink: 0;
        }

        .feedback-line {
            font-family: var(--font-mono);
            text-align: center;
            font-size: 1rem;
            font-weight: 700;
            min-height: 24px;
            text-transform: uppercase;
        }

        .text-success { color: var(--accent-green); }
        .text-error { color: var(--accent-red); }

        .quip-line {
            font-family: var(--font-display);
            text-align: center;
            font-size: 0.92rem;
            font-style: italic;
            color: var(--text-secondary);
            min-height: 20px;
        }

        /* ---- Range gauge ---- */
        .gauge-outer {
            width: 100%;
            height: 16px;
            background: var(--panel-sunken);
            border: 1px solid var(--border-color);
            border-radius: 999px;
            overflow: hidden;
            margin-bottom: 16px;
        }

        .gauge-fill {
            height: 100%;
            background: var(--accent-teal);
            border-radius: 999px;
            transition: width 0.15s linear, background-color 0.3s ease;
        }

        .gauge-fill.warn { background: var(--accent-amber); }

        .gauge-fill.critical {
            background: var(--accent-red);
            animation: gaugePulse 0.9s ease-in-out infinite;
        }

        @keyframes gaugePulse {
            0%, 100% { opacity: 1; }
            50% { opacity: 0.55; }
        }

        /* ---- Road / car sprite ---- */
        .road-wrap {
            margin-bottom: 18px;
        }

        .road-track {
            position: relative;
            height: 56px;
            border-radius: 10px;
            border: 1px solid var(--border-color);
            background:
                repeating-linear-gradient(
                    90deg,
                    var(--border-color) 0px,
                    var(--border-color) 24px,
                    transparent 24px,
                    transparent 48px
                ),
                var(--panel-sunken);
            background-size: 100% 2px, 100% 100%;
            background-position: center;
            background-repeat: repeat-x, no-repeat;
            overflow: hidden;
        }

        .checkpoint-flags {
            position: absolute;
            inset: 0;
        }

        .road-flag {
            position: absolute;
            top: 4px;
            transform: translateX(-50%);
            font-size: 1rem;
            opacity: 0.55;
        }

        .road-flag.passed {
            opacity: 1;
            filter: saturate(1.3);
        }

        .car-sprite {
            position: absolute;
            bottom: 6px;
            left: 0;
            font-size: 1.7rem;
            transition: left 0.6s ease;
            transform: scaleX(-1);
        }

        /* ---- Typed numeric answer ---- */
        .numeric-row {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 12px;
            background: var(--card-bg);
            border: 1px solid var(--border-color);
            border-radius: 8px;
            padding: 16px;
        }

        .numeric-label {
            font-family: var(--font-mono);
            font-weight: 700;
            font-size: 0.9rem;
            color: var(--text-secondary);
        }

        .numeric-input {
            flex: 1 1 140px;
            min-width: 100px;
            font: inherit;
            font-family: var(--font-mono);
            font-weight: 700;
            font-size: 1.1rem;
            padding: 10px 14px;
            border-radius: 8px;
            border: 2px solid var(--border-color);
            background: var(--kit-input-bg);
            color: var(--text-primary);
            outline: none;
        }

        .numeric-input:focus-visible {
            border-color: var(--accent-teal);
        }

        .numeric-submit-btn {
            margin-top: 0;
            padding: 12px 22px;
            font-size: 0.85rem;
        }

        @media (max-width: 640px) {
            .numeric-row { flex-direction: column; align-items: stretch; }
        }

        /* ---- Number-line drag widget (domain/range + exclusion) ---- */
        .answer-zone {
            margin-bottom: 6px;
        }

        .nline-hint {
            font-size: 0.85rem;
            color: var(--text-secondary);
            margin-bottom: 10px;
            text-align: center;
        }

        .nline-wrap {
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .nline-endlabel {
            font-family: var(--font-mono);
            font-weight: 700;
            color: var(--text-secondary);
            font-size: 0.85rem;
            flex-shrink: 0;
        }

        .nline-track {
            position: relative;
            flex: 1 1 auto;
            height: 48px;
            cursor: pointer;
            touch-action: none;
        }

        .nline-baseline {
            position: absolute;
            left: 0;
            right: 0;
            top: 50%;
            height: 4px;
            transform: translateY(-50%);
            background: var(--border-color);
            border-radius: 999px;
        }

        .nline-fill {
            position: absolute;
            top: 50%;
            height: 8px;
            transform: translateY(-50%);
            background: var(--accent-teal);
            border-radius: 999px;
            opacity: 0.85;
        }

        .nline-handle {
            position: absolute;
            top: 50%;
            width: 20px;
            height: 20px;
            transform: translate(-50%, -50%);
            border-radius: 50%;
            background: var(--container-bg);
            border: 3px solid var(--accent-teal);
            cursor: pointer;
        }

        .nline-handle.closed {
            background: var(--accent-teal);
        }

        .nline-marker {
            position: absolute;
            top: 50%;
            width: 20px;
            height: 20px;
            transform: translate(-50%, -50%);
            border-radius: 50%;
            background: var(--accent-red);
            border: 3px solid var(--accent-red);
        }

        .nline-bubble {
            position: absolute;
            top: -26px;
            left: 50%;
            transform: translateX(-50%);
            font-family: var(--font-mono);
            font-size: 0.78rem;
            font-weight: 700;
            color: var(--text-primary);
            background: var(--card-bg);
            border: 1px solid var(--border-color);
            border-radius: 6px;
            padding: 2px 6px;
            white-space: nowrap;
        }

        .nline-readout {
            font-family: var(--font-mono);
            text-align: center;
            font-size: 0.95rem;
            font-weight: 700;
            color: var(--accent-teal);
            margin: 14px 0 8px;
        }

        .nline-confirm-btn {
            width: 100%;
            margin-top: 6px;
        }

        .nline-confirm-btn:disabled {
            opacity: 0.5;
            cursor: not-allowed;
        }

        .screen-center {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            text-align: center;
            padding: 10px 0;
        }

        .action-btn {
            background: var(--accent-teal);
            color: #00232b;
            border: none;
            padding: 14px 36px;
            font-family: var(--font-display);
            font-size: 1rem;
            font-weight: 800;
            text-transform: uppercase;
            letter-spacing: 1px;
            cursor: pointer;
            margin-top: 20px;
            border-radius: 8px;
            box-shadow: 0 4px 12px var(--shadow-color);
        }

        .action-btn:hover {
            opacity: 0.9;
        }

        .brief-box {
            background: var(--card-bg);
            border: 1px solid var(--border-color);
            padding: 20px 28px;
            text-align: left;
            margin: 20px 0;
            max-width: 680px;
            line-height: 1.7;
            font-size: 0.95rem;
            border-radius: 8px;
        }

        .brief-box ul {
            padding-left: 20px;
        }

        .brief-box li {
            margin-bottom: 8px;
        }

        footer {
            margin-top: 24px;
            font-family: var(--font-mono);
            font-size: 0.8rem;
            color: var(--text-secondary);
            text-align: center;
            letter-spacing: 0.5px;
        }