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

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            min-height: 100vh;
            padding: 40px 20px;
        }

        .container {
            max-width: 900px;
            margin: 0 auto;
            background: rgba(255, 255, 255, 0.98);
            border-radius: 25px;
            padding: 50px 40px;
            box-shadow: 0 25px 70px rgba(0, 0, 0, 0.3);
        }

        h1 {
            text-align: center;
            color: #2d3748;
            font-size: 2.8em;
            margin-bottom: 15px;
            font-weight: 700;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
        }

        .subtitle {
            text-align: center;
            color: #718096;
            font-size: 1.1em;
            margin-bottom: 40px;
        }

        .topics-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(380px, 1fr));
            gap: 20px;
            list-style: none;
        }

        .topic-card {
            background: white;
            padding: 25px;
            border-radius: 16px;
            box-shadow: 0 4px 15px rgba(0, 0, 0, 0.08);
            transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
            cursor: pointer;
            position: relative;
            overflow: hidden;
            border: 2px solid transparent;
        }

        .topic-card::before {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            width: 5px;
            height: 100%;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            transition: width 0.4s ease;
        }

        .topic-card:hover::before {
            width: 100%;
            opacity: 0.1;
        }

        .topic-card:hover {
            transform: translateY(-8px) scale(1.02);
            box-shadow: 0 15px 40px rgba(102, 126, 234, 0.3);
            border-color: #667eea;
        }

        .topic-header {
            display: flex;
            align-items: center;
            gap: 15px;
            margin-bottom: 12px;
        }

        .topic-number {
            font-size: 1.5em;
            font-weight: 700;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            min-width: 40px;
        }

        .topic-icon {
            font-size: 1.8em;
            filter: grayscale(0.3);
            transition: all 0.3s ease;
        }

        .topic-card:hover .topic-icon {
            filter: grayscale(0);
            transform: scale(1.15) rotate(5deg);
        }

        .topic-text {
            font-size: 1.15em;
            font-weight: 600;
            color: #2d3748;
            line-height: 1.4;
            flex: 1;
        }

        .topic-description {
            font-size: 0.9em;
            color: #718096;
            line-height: 1.6;
            margin-top: 8px;
            padding-left: 55px;
        }

        .difficulty {
            display: inline-block;
            padding: 4px 12px;
            border-radius: 20px;
            font-size: 0.75em;
            font-weight: 600;
            margin-top: 10px;
            margin-left: 55px;
        }

        .beginner {
            background: #d4edda;
            color: #155724;
        }

        .intermediate {
            background: #fff3cd;
            color: #856404;
        }

        .advanced {
            background: #f8d7da;
            color: #721c24;
        }

        @media (max-width: 768px) {
            .container {
                padding: 30px 20px;
            }

            h1 {
                font-size: 2em;
            }

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

            .topic-card {
                padding: 20px;
            }
        }