:root {
            --primary-color: #6a4cff;
            --secondary-color: #8ec5fc;
            --accent-color: #ff9a8b;
            --text-color: #333;
            --light-bg: #f8f9fa;
            --letter-bg: #9d8ee2;
            --correct-color: #4CAF50;
            --incorrect-color: #f44336;
            --current-level: #FF9800;
        }
        
        * {
            box-sizing: border-box;
        }
        
        body {
            font-family: 'Poppins', Arial, sans-serif;
            margin: 0;
            padding: 0;
            display: flex;
            flex-direction: column;
            align-items: center;
            min-height: 100vh;
            background: linear-gradient(135deg, #f5f7fa 0%, #e4e8f0 100%);
            color: var(--text-color);
            position: relative;
            padding-bottom: 150px;
        }
        
        .header {
            width: 100%;
            padding: 15px 20px;
            display: flex;
            align-items: center;
            justify-content: space-between;
            background-color: white;
            box-shadow: 0 2px 10px rgba(0,0,0,0.1);
        }
        
        .back-button {
            background-color: transparent;
            border: none;
            cursor: pointer;
            font-size: 20px;
            padding: 8px;
            color: var(--primary-color);
            border-radius: 50%;
            width: 40px;
            height: 40px;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: all 0.2s ease;
        }
        
        .back-button:hover {
            background-color: #f3f4f6;
        }
        
        
        h1 {
            text-align: center;
            font-size: 1.8rem;
            margin: 20px 0;
            color: var(--primary-color);
            text-shadow: 0 2px 4px rgba(106, 76, 255, 0.1);
        }
        
        .current-letter-display {
            font-size: 5rem;
            font-weight: bold;
            color: var(--primary-color);
            margin: 20px 0;
            text-align: center;
            min-height: 100px;
            display: flex;
            align-items: center;
            justify-content: center;
        }
        
        .play-controls {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 20px;
            margin-bottom: 30px;
        }
        
        .play-button {
            background-color: var(--primary-color);
            color: white;
            border: none;
            border-radius: 50%;
            width: 80px;
            height: 80px;
            cursor: pointer;
            font-weight: 600;
            font-size: 1.2rem;
            transition: all 0.3s ease;
            box-shadow: 0 4px 8px rgba(106, 76, 255, 0.3);
            display: flex;
            align-items: center;
            justify-content: center;
        }
        
        .play-button:hover {
            background-color: #5a3ce6;
            transform: translateY(-2px);
            box-shadow: 0 6px 12px rgba(106, 76, 255, 0.4);
        }
        
        .play-button:active {
            transform: translateY(0);
        }
        
        .play-button i {
            font-size: 2rem;
        }
        
        .answer-buttons {
            display: flex;
            gap: 15px;
        }
        
        .answer-btn {
            padding: 12px 25px;
            border-radius: 25px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            border: none;
            font-size: 1rem;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }
        
        .correct-btn {
            background-color: var(--correct-color);
            color: white;
        }
        
        .incorrect-btn {
            background-color: var(--incorrect-color);
            color: white;
        }
        
        .correct-btn:hover {
            background-color: #3d8b40;
            transform: translateY(-2px);
        }
        
        .incorrect-btn:hover {
            background-color: #d32f2f;
            transform: translateY(-2px);
        }
        
        .letter-progress {
            width: 100%;
            max-width: 800px;
            margin: 0 auto;
            padding: 20px;
        }
        
        .letter-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(80px, 1fr));
            gap: 10px;
            width: 100%;
        }
        
        .letter-card {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 8px;
            background-color: white;
            border-radius: 10px;
            padding: 10px;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }
        
        .letter {
            background-color: var(--letter-bg);
            width: 50px;
            height: 50px;
            border-radius: 10px;
            display: flex;
            justify-content: center;
            align-items: center;
            font-size: 1.5rem;
            font-weight: bold;
            color: white;
        }
        
        .status-indicator {
            font-size: 1.2rem;
        }
        
        .correct {
            color: var(--correct-color);
        }
        
        .incorrect {
            color: var(--incorrect-color);
        }
        
        .navigation {
            position: fixed;
            bottom: 0;
            left: 0;
            right: 0;
            display: flex;
            justify-content: flex-end;
            padding: 15px 20px;
            background-color: white;
            box-shadow: 0 -2px 10px rgba(0,0,0,0.1);
            z-index: 100;
        }
        
        .nav-button {
            padding: 12px 25px;
            border-radius: 25px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            border: none;
            font-size: 1rem;
            display: flex;
            align-items: center;
            gap: 8px;
        }
        
        .next-nav {
            background: linear-gradient(145deg, var(--primary-color), var(--secondary-color));
            color: white;
            box-shadow: 0 2px 8px rgba(106, 76, 255, 0.3);
        }
        
        .next-nav:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(106, 76, 255, 0.4);
        }
        
        .completion-message {
            text-align: center;
            font-size: 1.2rem;
            color: var(--primary-color);
            font-weight: 600;
            margin: 20px 0;
            opacity: 0;
            transition: opacity 0.5s ease;
            height: 0;
            overflow: hidden;
        }
        
        .completion-message.show {
            opacity: 1;
            height: auto;
        }
        
        .score-display {
            position: absolute;
            right: 20px;
            top: 20px;
            background-color: white;
            padding: 10px 15px;
            border-radius: 20px;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
            font-weight: 600;
            color: var(--primary-color);
        }
        
        /* Custom Alert Styles */
        .custom-alert {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background-color: rgba(0,0,0,0.5);
            z-index: 1000;
            justify-content: center;
            align-items: center;
        }
        
        .alert-content {
            background-color: white;
            padding: 25px;
            border-radius: 15px;
            width: 90%;
            max-width: 400px;
            box-shadow: 0 5px 15px rgba(0,0,0,0.2);
            text-align: center;
            animation: alertFadeIn 0.3s ease;
        }
        
        @keyframes alertFadeIn {
            from { opacity: 0; transform: translateY(-20px); }
            to { opacity: 1; transform: translateY(0); }
        }
        
        .alert-title {
            font-size: 1.4rem;
            color: var(--primary-color);
            margin-bottom: 15px;
            font-weight: 600;
        }
        
        .alert-message {
            font-size: 1rem;
            color: var(--text-color);
            margin-bottom: 25px;
        }
        
        .alert-buttons {
            display: flex;
            justify-content: center;
            gap: 15px;
        }
        
        .alert-btn {
            padding: 10px 25px;
            border-radius: 25px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            border: none;
            font-size: 1rem;
        }
        
        .alert-confirm {
            background-color: var(--primary-color);
            color: white;
        }
        
        .alert-cancel {
            background-color: #e0e0e0;
            color: var(--text-color);
        }
        
        .alert-confirm:hover {
            background-color: #5a3ce6;
        }
        
        .alert-cancel:hover {
            background-color: #d0d0d0;
        }
        
        @media (max-width: 600px) {
            h1 {
                font-size: 1.5rem;
            }
            
            .current-letter-display {
                font-size: 4rem;
            }
            
            .play-button {
                width: 70px;
                height: 70px;
            }
            
            .answer-buttons {
                flex-direction: column;
                width: 100%;
                align-items: center;
            }
            
            .answer-btn {
                width: 80%;
            }
            
            .letter-grid {
                grid-template-columns: repeat(auto-fill, minmax(70px, 1fr));
            }
            
            .score-display {
                top: 10px;
                right: 10px;
                font-size: 0.9rem;
            }
        }