:root {
            --bg-main: #0f172a;
            --bg-surface: #1e293b;
            --bg-surface-hover: #334155;
            --text-main: #f8fafc;
            --text-muted: #94a3b8;
            --primary: #3b82f6;
            --primary-hover: #2563eb;
            --accent: #10b981;
            --color-x: #ef4444;
            --color-o: #3b82f6;
            --border-radius: 12px;
            --transition-speed: 0.25s;
            --font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
        }

        [data-theme="light"] {
            --bg-main: #f1f5f9;
            --bg-surface: #ffffff;
            --bg-surface-hover: #e2e8f0;
            --text-main: #0f172a;
            --text-muted: #64748b;
            --primary: #2563eb;
            --primary-hover: #1d4ed8;
        }

        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            font-family: var(--font-family);
        }

        body {
            background-color: var(--bg-main);
            color: var(--text-main);
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            overflow-x: hidden;
            position: relative;
            background-size: cover;
            background-position: center;
            background-repeat: no-repeat;
        }

        #wallpaper-overlay {
            position: absolute;
            top: 0; left: 0; width: 100%; height: 100%;
            background: rgba(15, 23, 42, 0.75);
            z-index: 0;
            display: none;
            pointer-events: none;
        }

        body.has-wallpaper #wallpaper-overlay {
            display: block;
        }

        .app-container {
            position: relative;
            z-index: 1;
            width: 100%;
            max-width: 600px;
            padding: 20px;
            display: flex;
            flex-direction: column;
            gap: 20px;
        }

        .screen {
            background: var(--bg-surface);
            padding: 30px;
            border-radius: var(--border-radius);
            box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.3);
            display: none;
            flex-direction: column;
            gap: 24px;
            transition: opacity var(--transition-speed) ease;
        }

        .screen.active {
            display: flex;
        }

        h1, h2, h3 {
            text-align: center;
            font-weight: 800;
            letter-spacing: -0.025em;
        }

        h1 { font-size: clamp(1.8rem, 5vw, 2.5rem); color: var(--primary); }
        h2 { font-size: clamp(1.4rem, 4vw, 1.8rem); }

        .form-group {
            display: flex;
            flex-direction: column;
            gap: 8px;
        }

        label {
            font-size: 0.9rem;
            font-weight: 600;
            color: var(--text-muted);
        }

        select, input[type="text"], button {
            width: 100%;
            padding: 12px 16px;
            border-radius: 8px;
            border: 2px solid transparent;
            background: var(--bg-surface-hover);
            color: var(--text-main);
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: all var(--transition-speed) ease;
        }

        select:focus, button:focus {
            outline: none;
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.4);
        }

        button.btn-primary {
            background: var(--primary);
            color: #ffffff;
        }
        button.btn-primary:hover { background: var(--primary-hover); }

        button.btn-secondary {
            background: transparent;
            border: 2px solid var(--bg-surface-hover);
        }
        button.btn-secondary:hover { background: var(--bg-surface-hover); }

        .color-pickers {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 16px;
        }

        .color-input-wrapper {
            display: flex;
            align-items: center;
            gap: 10px;
            background: var(--bg-surface-hover);
            padding: 8px 12px;
            border-radius: 8px;
        }

        input[type="color"] {
            border: none;
            width: 40px;
            height: 40px;
            border-radius: 6px;
            cursor: pointer;
            background: transparent;
        }

        /* Toss Animation Layout */
        .coin-container {
            perspective: 1000px;
            width: 120px;
            height: 120px;
            margin: 20px auto;
        }

        .coin {
            width: 100%;
            height: 100%;
            position: relative;
            transform-style: preserve-3d;
            transition: transform 2s cubic-bezier(0.175, 0.885, 0.32, 1.275);
        }

        .coin-side {
            position: absolute;
            width: 100%;
            height: 100%;
            border-radius: 50%;
            backface-visibility: hidden;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 2rem;
            font-weight: 800;
            color: #fff;
        }

        .coin-front { background: linear-gradient(135deg, #f59e0b, #d97706); }
        .coin-back { background: linear-gradient(135deg, #3b82f6, #1d4ed8); transform: rotateY(180deg); }

        /* Board Grid Management */
        .game-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .status-announcer {
            font-size: 1.2rem;
            font-weight: 700;
            text-align: center;
            min-height: 1.8rem;
        }

        .board-container {
            width: 100%;
            aspect-ratio: 1 / 1;
            display: grid;
            gap: 10px;
            background: var(--bg-surface-hover);
            padding: 10px;
            border-radius: var(--border-radius);
            position: relative;
        }

        .cell {
            background: var(--bg-surface);
            border-radius: 8px;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: calc(100% + 2vw);
            font-weight: 800;
            cursor: pointer;
            transition: background var(--transition-speed) ease, transform 0.1s ease;
            user-select: none;
            outline: none;
        }

        .cell:focus-visible {
            box-shadow: 0 0 0 4px var(--primary);
        }

        .cell.occupied {
            cursor: not-allowed;
        }

        .cell .piece {
            animation: pieceAppear 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275) forwards;
            display: inline-block;
        }

        @keyframes pieceAppear {
            0% { transform: scale(0); opacity: 0; }
            100% { transform: scale(1); opacity: 1; }
        }

        .cell.last-move {
            box-shadow: inset 0 0 0 3px var(--primary);
        }

        .cell.winning-cell {
            background: var(--accent) !important;
            color: white !important;
        }

        /* History Panel */
        .history-controls {
            display: flex;
            gap: 10px;
            justify-content: center;
        }

        .history-controls button {
            width: auto;
            flex: 1;
        }

        /* Statistics Layout */
        .stats-grid {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 12px;
        }

        .stat-card {
            background: var(--bg-surface-hover);
            padding: 12px;
            border-radius: 8px;
            text-align: center;
        }

        .stat-val {
            font-size: 1.5rem;
            font-weight: 800;
            color: var(--primary);
        }

        .stat-lbl {
            font-size: 0.8rem;
            color: var(--text-muted);
            text-transform: uppercase;
            font-weight: 700;
        }

        /* Audio & Control Bars */
        .utility-bar {
            display: flex;
            justify-content: space-between;
            gap: 10px;
        }

        .utility-bar button { width: auto; padding: 8px 12px; font-size: 0.9rem; }

        /* Modal Overlay System */
        .modal-overlay {
            position: fixed;
            top: 0; left: 0; width: 100%; height: 100%;
            background: rgba(0,0,0,0.6);
            backdrop-filter: blur(4px);
            z-index: 100;
            display: none;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        .modal {
            background: var(--bg-surface);
            padding: 24px;
            border-radius: var(--border-radius);
            max-width: 400px;
            width: 100%;
            display: flex;
            flex-direction: column;
            gap: 16px;
        }

        /* Particle Overlay Canvas */
        #particles-canvas {
            position: fixed;
            top: 0; left: 0; width: 100%; height: 100%;
            pointer-events: none;
            z-index: 99;
        }

        .sr-only {
            position: absolute;
            width: 1px;
            height: 1px;
            padding: 0;
            margin: -1px;
            overflow: hidden;
            clip: rect(0, 0, 0, 0);
            border: 0;
        }

        @media (prefers-reduced-motion: reduce) {
            * {
                animation-duration: 0s !important;
                transition-duration: 0s !important;
            }
            .coin { transition: none !important; }
        }