* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            line-height: 1.6;
            color: #333;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            min-height: 100vh;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 20px;
        }

        header {
            background: rgba(255, 255, 255, 0.1);
            backdrop-filter: blur(10px);
            padding: 1rem 0;
            position: fixed;
            width: 100%;
            top: 0;
            z-index: 1000;
            box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
        }

        nav {
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .logo {
            font-size: 1.8rem;
            font-weight: bold;
            color: white;
            text-decoration: none;
        }

        .nav-links {
            display: flex;
            list-style: none;
            gap: 2rem;
        }

        .nav-links a {
            color: white;
            text-decoration: none;
            transition: all 0.3s ease;
            padding: 0.5rem 1rem;
            border-radius: 25px;
        }

        .nav-links a:hover {
            background: rgba(255, 255, 255, 0.2);
            transform: translateY(-2px);
        }

        .auth-buttons {
            display: flex;
            gap: 1rem;
        }

        .btn {
            padding: 0.7rem 1.5rem;
            border: none;
            border-radius: 25px;
            cursor: pointer;
            text-decoration: none;
            transition: all 0.3s ease;
            font-weight: 600;
            display: inline-block;
        }

        .btn-primary {
            background: #ff6b6b;
            color: white;
        }

        .btn-secondary {
            background: transparent;
            color: white;
            border: 2px solid white;
        }

        .btn:hover {
            transform: translateY(-3px);
            box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
        }

        .btn-primary:hover {
            background: #ff5252;
        }

        .btn-secondary:hover {
            background: white;
            color: #667eea;
        }

        main {
            padding-top: 100px;
            min-height: 100vh;
        }

        .hero {
            text-align: center;
            padding: 4rem 0;
            color: white;
        }

        .hero h1 {
            font-size: 3.5rem;
            margin-bottom: 1rem;
            animation: fadeInUp 1s ease;
        }

        .hero p {
            font-size: 1.2rem;
            margin-bottom: 2rem;
            opacity: 0.9;
            animation: fadeInUp 1s ease 0.2s both;
        }

        .hero-buttons {
            display: flex;
            gap: 1rem;
            justify-content: center;
            margin-top: 2rem;
            animation: fadeInUp 1s ease 0.4s both;
        }

        .features {
            background: white;
            padding: 4rem 0;
            margin-top: 3rem;
            border-radius: 30px 30px 0 0;
        }

        .features h2 {
            text-align: center;
            font-size: 2.5rem;
            margin-bottom: 3rem;
            color: #333;
        }

        .feature-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 2rem;
            margin-bottom: 3rem;
        }

        .feature-card {
            background: linear-gradient(135deg, #667eea, #764ba2);
            color: white;
            padding: 2rem;
            border-radius: 20px;
            text-align: center;
            transition: transform 0.3s ease;
            cursor: pointer;
        }

        .feature-card:hover {
            transform: translateY(-10px);
        }

        .feature-icon {
            font-size: 3rem;
            margin-bottom: 1rem;
        }

        .feature-card h3 {
            margin-bottom: 1rem;
            font-size: 1.5rem;
        }

        .levels {
            padding: 3rem 0;
            background: #f8f9fa;
        }

        .levels h2 {
            text-align: center;
            margin-bottom: 2rem;
            color: #333;
        }

        .level-cards {
            display: flex;
            gap: 1rem;
            justify-content: center;
            flex-wrap: wrap;
        }

        .level-card {
            background: white;
            padding: 1.5rem;
            border-radius: 15px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            text-align: center;
            min-width: 200px;
            transition: all 0.3s ease;
        }

        .level-card:hover {
            transform: translateY(-5px);
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.15);
        }

        .level-badge {
            display: inline-block;
            padding: 0.5rem 1rem;
            border-radius: 25px;
            color: white;
            font-weight: bold;
            margin-bottom: 1rem;
        }

        .beginner { background: #4CAF50; }
        .intermediate { background: #FF9800; }
        .advanced { background: #F44336; }

        .stats {
            background: linear-gradient(135deg, #667eea, #764ba2);
            color: white;
            padding: 3rem 0;
            text-align: center;
        }

        .stats-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 2rem;
        }

        .stat-item h3 {
            font-size: 3rem;
            margin-bottom: 0.5rem;
        }

        .modal {
            display: none;
            position: fixed;
            z-index: 2000;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            background: rgba(0, 0, 0, 0.5);
        }

        .modal-content {
            background: white;
            margin: 5% auto;
            padding: 2rem;
            border-radius: 20px;
            width: 90%;
            max-width: 400px;
            position: relative;
            animation: slideIn 0.3s ease;
        }

        .close {
            position: absolute;
            right: 1rem;
            top: 1rem;
            font-size: 2rem;
            cursor: pointer;
            color: #999;
        }

        .close:hover {
            color: #333;
        }

        .form-group {
            margin-bottom: 1rem;
        }

        .form-group label {
            display: block;
            margin-bottom: 0.5rem;
            font-weight: 600;
        }

        .form-group input {
            width: 100%;
            padding: 0.8rem;
            border: 2px solid #e1e1e1;
            border-radius: 10px;
            font-size: 1rem;
        }

        .form-group input:focus {
            outline: none;
            border-color: #667eea;
        }

        .quiz-container {
            background: white;
            padding: 2rem;
            margin: 2rem 0;
            border-radius: 15px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            display: none;
        }

        .quiz-container.active {
            display: block;
        }

        .question {
            margin-bottom: 1rem;
        }

        .options {
            display: grid;
            gap: 0.5rem;
            margin-bottom: 1rem;
        }

        .option {
            background: #f8f9fa;
            padding: 0.8rem;
            border-radius: 8px;
            cursor: pointer;
            transition: background 0.3s ease;
        }

        .option:hover {
            background: #e9ecef;
        }

        .option.selected {
            background: #667eea;
            color: white;
        }

        .leaderboard {
            background: white;
            padding: 2rem;
            border-radius: 15px;
            margin: 2rem 0;
            display: none;
        }

        .leaderboard.active {
            display: block;
        }

        .leaderboard-item {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 1rem;
            border-bottom: 1px solid #e1e1e1;
        }

        .leaderboard-item:last-child {
            border-bottom: none;
        }

        .rank {
            font-weight: bold;
            color: #667eea;
        }

        footer {
            background: #333;
            color: white;
            text-align: center;
            padding: 2rem 0;
        }

        @keyframes fadeInUp {
            from {
                opacity: 0;
                transform: translateY(30px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        @keyframes slideIn {
            from {
                transform: scale(0.7);
                opacity: 0;
            }
            to {
                transform: scale(1);
                opacity: 1;
            }
        }

        @media (max-width: 768px) {
            .nav-links {
                display: none;
            }

            .hero h1 {
                font-size: 2.5rem;
            }

            .hero-buttons {
                flex-direction: column;
                align-items: center;
            }

            .feature-grid {
                grid-template-columns: 1fr;
            }
        }