:root {
            --dark-bg: #1E1E1E;
            --neon-green: #39FF14;
            --turquoise: #00E3E3;
            --purple: #FF00FF;
            --azure: #00FFFF;
            --pink: #FF00AA;
            --corner-radius: 12px;
            --glow-intensity: 0.7;
        }
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Inter', 'SF Pro', sans-serif;
        }
        
        body {
            background-color: var(--dark-bg);
            color: white;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            overflow: hidden;
        }
        
        .container {
            display: flex;
            flex-direction: column;
            height: 100vh;
            padding: 20px;
            max-width: 1200px;
            margin: 0 auto;
            width: 100%;
        }
        
        .header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 20px;
        }
        
        .app-title {
            font-size: 1.5rem;
            font-weight: 500;
            color: var(--neon-green);
            text-shadow: 0 0 10px rgba(57, 255, 20, var(--glow-intensity));
        }
        
        .audio-section {
            flex: 1;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            margin-bottom: 20px;
            position: relative;
        }
        
        .audio-visualizer {
            width: 200px;
            height: 200px;
            border-radius: 50%;
            border: 2px solid var(--azure);
            box-shadow: 0 0 15px rgba(0, 255, 255, var(--glow-intensity));
            display: flex;
            align-items: center;
            justify-content: center;
            position: relative;
            overflow: hidden;
            transition: all 0.3s ease;
        }
        
        .audio-visualizer.active {
            box-shadow: 0 0 30px rgba(0, 255, 255, 0.9);
        }
        
        .audio-letter {
            font-size: 5rem;
            font-weight: 500;
            color: white;
            text-shadow: 0 0 15px rgba(255, 255, 255, var(--glow-intensity));
            transition: all 0.3s ease;
        }
        
        .audio-waves {
            position: absolute;
            width: 100%;
            height: 100%;
            display: flex;
            align-items: center;
            justify-content: center;
            opacity: 0;
            transition: opacity 0.3s ease;
        }
        
        .audio-waves.active {
            opacity: 1;
        }
        
        .wave {
            position: absolute;
            border: 2px solid var(--turquoise);
            border-radius: 50%;
            animation: wave-animation 2s infinite;
            opacity: 0;
        }
        
        .wave:nth-child(1) {
            width: 30%;
            height: 30%;
            animation-delay: 0s;
        }
        
        .wave:nth-child(2) {
            width: 50%;
            height: 50%;
            animation-delay: 0.3s;
        }
        
        .wave:nth-child(3) {
            width: 70%;
            height: 70%;
            animation-delay: 0.6s;
        }
        
        .wave:nth-child(4) {
            width: 90%;
            height: 90%;
            animation-delay: 0.9s;
        }
        
        @keyframes wave-animation {
            0% {
                transform: scale(0.5);
                opacity: 0.8;
            }
            100% {
                transform: scale(1.2);
                opacity: 0;
            }
        }
        
        .current-letter-info {
            margin-top: 20px;
            text-align: center;
            opacity: 0;
            transform: translateY(20px);
            transition: all 0.3s ease;
        }
        
        .current-letter-info.active {
            opacity: 1;
            transform: translateY(0);
        }
        
        .letter-name {
            font-size: 1.2rem;
            color: var(--turquoise);
            margin-bottom: 5px;
            text-shadow: 0 0 10px rgba(0, 227, 227, var(--glow-intensity));
        }
        
        .letter-example {
            font-size: 1rem;
            color: white;
            opacity: 0.8;
        }
        
        .alphabet-section {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(60px, 1fr));
            gap: 15px;
            padding: 20px;
            border-top: 1px solid rgba(0, 227, 227, 0.3);
            background: rgba(30, 30, 30, 0.7);
            border-radius: var(--corner-radius) var(--corner-radius) 0 0;
            box-shadow: 0 -5px 15px rgba(0, 0, 0, 0.3);
        }
        
        .letter-btn {
            display: flex;
            align-items: center;
            justify-content: center;
            height: 60px;
            background-color: rgba(57, 255, 20, 0.1);
            border: 1px solid var(--azure);
            border-radius: var(--corner-radius);
            color: white;
            font-size: 1.5rem;
            font-weight: 500;
            cursor: pointer;
            transition: all 0.2s ease;
            box-shadow: 0 0 10px rgba(0, 255, 255, 0.2);
            position: relative;
            overflow: hidden;
        }
        
        .letter-btn:hover {
            background-color: rgba(57, 255, 20, 0.2);
            box-shadow: 0 0 15px rgba(0, 255, 255, 0.5);
            transform: translateY(-2px);
        }
        
        .letter-btn:active, .letter-btn.active {
            background-color: rgba(57, 255, 20, 0.3);
            box-shadow: 0 0 20px rgba(0, 255, 255, 0.8);
            transform: translateY(0);
        }
        
        .letter-btn::after {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: linear-gradient(45deg, transparent, rgba(255, 255, 255, 0.1), transparent);
            transform: translateX(-100%);
            transition: transform 0.3s ease;
        }
        
        .letter-btn:hover::after {
            transform: translateX(100%);
        }
        
        @media (max-width: 768px) {
            .alphabet-section {
                grid-template-columns: repeat(auto-fit, minmax(45px, 1fr));
                gap: 10px;
            }
            
            .letter-btn {
                height: 50px;
                font-size: 1.2rem;
            }
            
            .audio-visualizer {
                width: 150px;
                height: 150px;
            }
            
            .audio-letter {
                font-size: 4rem;
            }
        }
        
        @media (max-width: 480px) {
            .alphabet-section {
                grid-template-columns: repeat(auto-fit, minmax(40px, 1fr));
                gap: 8px;
            }
            
            .letter-btn {
                height: 45px;
                font-size: 1rem;
            }
            
            .audio-visualizer {
                width: 120px;
                height: 120px;
            }
            
            .audio-letter {
                font-size: 3rem;
            }
        }