:root {
            --primary: #00ffff;
            --primary-dim: #0891b2;
            --success: #00ff88;
            --danger: #ff2d55;
            --warn: #ffcc00;
            --bg-dark: rgba(0, 10, 20, 0.85);
            --glass: rgba(0, 255, 255, 0.1);
            --easy: #00ff88;
            --medium: #ffcc00;
            --hard: #ff2d55;
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Kanit', 'Outfit', sans-serif;
            user-select: none;
            -webkit-tap-highlight-color: transparent;
        }

        #question-text {
            font-family: 'Fira Code', 'Kanit', monospace !important;
            color: #ffffff !important;
            font-size: 1.45rem !important;
            font-weight: 700 !important;
            line-height: 1.5 !important;
            text-shadow: 0 2px 10px rgba(0, 0, 0, 0.9), 0 0 12px rgba(0, 255, 255, 0.3) !important;
            z-index: 5;
            position: relative;
        }

        html, body {
            background-color: #000;
            color: white;
            overflow: hidden;
            width: 100vw;
            height: 100vh;
            overscroll-behavior: none;
        }

        /* 1. Video Layer */
        #webcam {
            position: absolute;
            top: 0; left: 0;
            width: 100vw; height: 100vh;
            object-fit: cover;
            transform: scaleX(-1);
            z-index: 1;
            background: #010409;
        }

        /* subtle circuit-grid overlay for AR feel */
        #grid-overlay {
            position: absolute;
            top: 0; left: 0; width: 100%; height: 100%;
            z-index: 2;
            pointer-events: none;
            background-image:
                linear-gradient(rgba(0,255,255,0.05) 1px, transparent 1px),
                linear-gradient(90deg, rgba(0,255,255,0.05) 1px, transparent 1px);
            background-size: 40px 40px;
            mix-blend-mode: screen;
            opacity: 0.5;
        }

        /* 2. AR Visual Layer */
        #ui-layer {
            position: absolute;
            top: 0; left: 0;
            width: 100%; height: 100%;
            z-index: 10;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            background: radial-gradient(circle, transparent 25%, rgba(0,0,0,0.75) 100%);
        }

        #status-bar {
            position: absolute;
            top: 16px; left: 50%;
            transform: translateX(-50%);
            background: rgba(10, 18, 30, 0.92);
            border: 1px solid var(--primary);
            padding: 8px 18px;
            border-radius: 20px;
            text-align: center;
            font-weight: bold;
            font-size: 0.85rem;
            letter-spacing: 0.5px;
            text-shadow: 0 0 5px var(--primary);
            box-shadow: 0 4px 16px rgba(0, 0, 0, 0.5), 0 0 10px var(--glass);
            z-index: 20;
            backdrop-filter: blur(8px);
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .status-dot {
            display: inline-block;
            width: 10px; height: 10px;
            border-radius: 50%;
            background-color: var(--danger);
            box-shadow: 0 0 5px var(--danger);
            flex-shrink: 0;
        }
        .status-dot.active { background-color: var(--success); box-shadow: 0 0 5px var(--success); }

        #mute-btn {
            background: none;
            border: 1px solid var(--primary);
            color: var(--primary);
            border-radius: 50%;
            width: 26px; height: 26px;
            font-size: 0.8rem;
            cursor: pointer;
            display: flex; align-items: center; justify-content: center;
            line-height: 1;
            pointer-events: auto;
            transition: all 0.2s ease;
        }
        #mute-btn:hover {
            background: rgba(0, 255, 255, 0.2);
            box-shadow: 0 0 10px var(--primary);
        }

        .mode-toggle-btn {
            background: rgba(0, 240, 255, 0.15);
            border: 1px solid var(--primary);
            color: var(--primary);
            padding: 4px 12px;
            border-radius: 14px;
            font-size: 0.78rem;
            font-weight: 600;
            cursor: pointer;
            pointer-events: auto;
            transition: all 0.2s ease;
            white-space: nowrap;
        }
        .mode-toggle-btn:hover {
            background: var(--primary);
            color: #000;
            box-shadow: 0 0 12px var(--primary);
        }
        .mode-toggle-btn.mouse-mode {
            background: rgba(255, 183, 3, 0.2);
            border-color: #ffb703;
            color: #ffb703;
        }
        .mode-toggle-btn.mouse-mode:hover {
            background: #ffb703;
            color: #000;
            box-shadow: 0 0 12px #ffb703;
        }

        .screen {
            display: none;
            flex-direction: column;
            align-items: center;
            text-align: center;
            width: 100%;
            max-width: 650px;
            padding: 20px;
        }
        .screen.active { display: flex; animation: fadein 0.35s ease; }
        @keyframes fadein { from { opacity: 0; transform: translateY(8px);} to { opacity: 1; transform: translateY(0);} }

        h1 {
            font-family: 'Outfit', 'Kanit', sans-serif;
            font-size: 2.3rem;
            font-weight: 800;
            color: var(--primary);
            text-shadow: 0 0 12px var(--primary);
            margin-bottom: 6px;
            letter-spacing: 1px;
        }
        .subtitle { font-size: 1.05rem; margin-bottom: 30px; color: #8fe9e9; letter-spacing: 3px; font-weight: 600; }

        .hologram-box {
            background: rgba(8, 14, 28, 0.88);
            border: 2px solid var(--primary);
            padding: 22px 24px;
            border-radius: 14px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.7), inset 0 0 20px rgba(0,255,255,0.15), 0 0 20px rgba(0,255,255,0.2);
            backdrop-filter: blur(12px);
            margin-bottom: 18px;
            position: relative;
            overflow: hidden;
        }
        .hologram-box::before {
            content: "";
            position: absolute;
            top: -50%; left: -50%; width: 200%; height: 200%;
            background: linear-gradient(to bottom, transparent, rgba(0,255,255,0.06), transparent);
            animation: scanline 3s linear infinite;
            pointer-events: none;
        }
        @keyframes scanline { 0% { transform: translateY(-100%);} 100% { transform: translateY(100%);} }

        .hoverable {
            background: rgba(10, 18, 32, 0.88);
            border: 2px solid var(--primary);
            color: #ffffff;
            padding: 16px 28px;
            font-family: 'Fira Code', 'Kanit', sans-serif;
            font-size: 1.25rem;
            font-weight: 700;
            border-radius: 12px;
            margin: 6px;
            cursor: pointer;
            transition: transform 0.15s, box-shadow 0.15s, background 0.15s;
            position: relative;
            min-width: 190px;
            text-align: center;
            overflow: hidden;
            box-shadow: 0 4px 15px rgba(0, 0, 0, 0.5);
            text-shadow: 0 1px 4px rgba(0, 0, 0, 0.8);
        }
        .hoverable:active { transform: scale(0.97); }

        .answers-grid {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 14px;
            width: 100%;
            margin-top: 18px;
        }

        .hoverable.hovering {
            transform: scale(1.05);
            box-shadow: 0 0 18px var(--primary);
            background: rgba(0, 255, 255, 0.2);
        }
        /* fill sweep to visualize dwell progress on the button itself */
        .hoverable.hovering::after {
            content: "";
            position: absolute;
            left: 0; bottom: 0; height: 100%; width: var(--dwell, 0%);
            background: rgba(0,255,255,0.28);
            z-index: -1;
            transition: width 0.05s linear;
        }
        .correct-answer {
            border-color: var(--success) !important;
            box-shadow: 0 0 20px var(--success) !important;
            background: rgba(0, 255, 136, 0.25) !important;
        }
        .wrong-answer {
            border-color: var(--danger) !important;
            box-shadow: 0 0 20px var(--danger) !important;
            background: rgba(255, 45, 85, 0.25) !important;
            animation: shake 0.4s;
        }
        @keyframes shake { 0%, 100% { transform: translateX(0);} 25% { transform: translateX(-10px);} 75% { transform: translateX(10px);} }

        /* Difficulty buttons */
        .diff-grid { display: flex; gap: 12px; flex-wrap: wrap; justify-content: center; }
        .diff-btn { min-width: 150px; }
        .diff-btn[data-diff="easy"] { border-color: var(--easy); color: var(--easy); text-shadow: 0 0 6px var(--easy); }
        .diff-btn[data-diff="medium"] { border-color: var(--medium); color: var(--medium); text-shadow: 0 0 6px var(--medium); }
        .diff-btn[data-diff="hard"] { border-color: var(--hard); color: var(--hard); text-shadow: 0 0 6px var(--hard); }
        .diff-btn.hovering[data-diff="easy"] { background: rgba(0,255,136,0.2); box-shadow: 0 0 18px var(--easy); }
        .diff-btn.hovering[data-diff="medium"] { background: rgba(255,204,0,0.2); box-shadow: 0 0 18px var(--medium); }
        .diff-btn.hovering[data-diff="hard"] { background: rgba(255,45,85,0.2); box-shadow: 0 0 18px var(--hard); }

        #hud {
            position: absolute;
            top: 62px;
            width: 100%;
            padding: 0 18px;
            display: flex;
            flex-direction: column;
            gap: 6px;
            z-index: 15;
        }
        .hud-row { display: flex; justify-content: space-between; align-items: center; font-size: 1.05rem; font-weight: bold; }
        .hud-text { text-shadow: 1px 1px 2px black, 0 0 5px var(--primary); }
        #combo-text { color: #ffcc00; text-shadow: 0 0 10px #ffcc00; opacity: 0; transition: opacity 0.2s; }
        #combo-text.show { opacity: 1; }

        #level-dots { display: flex; gap: 6px; justify-content: center; margin-top: 4px; }
        .level-dot {
            width: 9px; height: 9px; border-radius: 50%;
            background: rgba(255,255,255,0.2);
            border: 1px solid var(--primary);
        }
        .level-dot.done { background: var(--success); box-shadow: 0 0 6px var(--success); }
        .level-dot.current { background: var(--primary); box-shadow: 0 0 8px var(--primary); }

        #timer-container {
            width: 100%; max-width: 400px; height: 10px;
            background: #222; border-radius: 5px;
            margin: 8px auto 0; overflow: hidden;
            border: 1px solid var(--primary);
        }
        #timer-bar {
            width: 100%; height: 100%;
            background: var(--primary);
            box-shadow: 0 0 10px var(--primary);
            transition: width 0.1s linear;
        }
        .timer-warning { background: var(--danger) !important; box-shadow: 0 0 10px var(--danger) !important; animation: pulse 0.5s infinite; }
        @keyframes pulse { 0% { opacity: 1;} 50% { opacity: 0.5;} 100% { opacity: 1;} }

        #notification {
            position: absolute;
            top: 50%; left: 50%;
            transform: translate(-50%, -50%);
            font-size: 2.6rem;
            font-weight: bold;
            text-align: center;
            opacity: 0;
            pointer-events: none;
            transition: opacity 0.3s, transform 0.3s;
            z-index: 50;
            text-shadow: 0 0 20px black;
        }
        #notification.show { opacity: 1; transform: translate(-50%, -50%) scale(1.08); }

        /* Particle burst for correct answers */
        #particle-layer {
            position: absolute; top: 0; left: 0; width: 100%; height: 100%;
            z-index: 40; pointer-events: none; overflow: hidden;
        }
        .particle {
            position: absolute;
            width: 8px; height: 8px;
            border-radius: 50%;
            background: var(--success);
            box-shadow: 0 0 8px var(--success);
            animation: burst 0.8s ease-out forwards;
        }
        @keyframes burst {
            to { transform: translate(var(--px), var(--py)) scale(0); opacity: 0; }
        }

        #hand-cursor {
            position: absolute;
            top: -50px; left: -50px;
            width: 60px; height: 60px;
            transform: translate(-50%, -50%);
            pointer-events: none;
            z-index: 100;
            display: none;
        }
        #cursor-ring { transform: rotate(-90deg); transform-origin: center; width: 100%; height: 100%; }
        #cursor-ring circle {
            fill: rgba(0, 255, 255, 0.2);
            stroke: var(--primary);
            stroke-width: 4;
            stroke-dasharray: 157;
            stroke-dashoffset: 157;
            transition: stroke-dashoffset 0.1s;
        }
        #hand-cursor.pinch #cursor-ring circle { stroke: var(--success); }
        #hand-cursor::after {
            content: "";
            position: absolute;
            top: 50%; left: 50%;
            width: 8px; height: 8px;
            background: white;
            border-radius: 50%;
            transform: translate(-50%, -50%);
            box-shadow: 0 0 10px white, 0 0 20px var(--primary);
        }

        .cta-box { background: rgba(0, 255, 136, 0.12); border: 1px solid var(--success); padding: 14px; margin-top: 16px; border-radius: 10px; font-size: 0.9rem; line-height: 1.5; }
        .stars { color: #ffeb3b; font-size: 1.8rem; letter-spacing: 5px; text-shadow: 0 0 10px #ffeb3b; }

        #leaderboard { width: 100%; margin-top: 14px; text-align: left; font-size: 0.9rem; }
        #leaderboard-list { list-style: none; margin-top: 6px; }
        #leaderboard-list li {
            display: flex; justify-content: space-between;
            padding: 6px 10px; border-bottom: 1px dashed rgba(0,255,255,0.25);
        }
        #leaderboard-list li.me { color: var(--warn); font-weight: bold; }

        .fallback-hint {
            font-size: 0.75rem; color: #7fd; margin-top: 6px; opacity: 0.8;
        }

        /* small screens */
        @media (max-width: 480px) {
            h1 { font-size: 1.7rem; }
            .hoverable { padding: 12px 14px; font-size: 0.95rem; min-width: 0; }
            #status-bar { font-size: 0.7rem; padding: 6px 12px; }
        }