:root {
            --bg-dark: #0f172a;
            --bg-card: #1e293b;
            --accent-shell: #22c55e;
            --accent-cpp: #3b82f6;
            --accent-python: #f59e0b;
            --text-primary: #f1f5f9;
            --text-secondary: #94a3b8;
        }

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

        body {
            font-family: 'JetBrains Mono', monospace;
            background: var(--bg-dark);
            color: var(--text-primary);
            min-height: 100vh;
            padding: 2rem;
        }

        .container {
            max-width: 1400px;
            margin: 0 auto;
        }

        .header {
            text-align: center;
            margin-bottom: 3rem;
            padding-bottom: 2rem;
            border-bottom: 2px solid rgba(255, 255, 255, 0.1);
        }

        h1 {
            font-size: 3rem;
            font-weight: 700;
            background: linear-gradient(135deg, #3b82f6, #8b5cf6, #ec4899);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            margin-bottom: 0.5rem;
        }

        .subtitle {
            color: var(--text-secondary);
            font-size: 1.1rem;
        }

        .language-section {
            margin-bottom: 3rem;
        }

        .language-title {
            font-size: 2rem;
            font-weight: 700;
            margin-bottom: 1.5rem;
            display: flex;
            align-items: center;
            gap: 1rem;
        }

        .shell-title { color: var(--accent-shell); }
        .cpp-title { color: var(--accent-cpp); }
        .python-title { color: --accent-python); }

        .cards-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
            gap: 1.5rem;
        }

        .level-card {
            background: var(--bg-card);
            border-radius: 16px;
            padding: 2rem;
            transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
            border: 2px solid transparent;
            cursor: pointer;
            text-decoration: none;
            color: inherit;
            display: block;
            position: relative;
            overflow: hidden;
        }

        .level-card::before {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            height: 4px;
            background: var(--card-accent);
            opacity: 0;
            transition: opacity 0.3s;
        }

        .level-card:hover::before {
            opacity: 1;
        }

        .level-card:hover {
            transform: translateY(-8px);
            border-color: var(--card-accent);
            box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4), 0 0 30px var(--card-accent-glow);
        }

        .shell-card {
            --card-accent: var(--accent-shell);
            --card-accent-glow: rgba(34, 197, 94, 0.2);
        }

        .cpp-card {
            --card-accent: var(--accent-cpp);
            --card-accent-glow: rgba(59, 130, 246, 0.2);
        }

        .python-card {
            --card-accent: var(--accent-python);
            --card-accent-glow: rgba(245, 158, 11, 0.2);
        }

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

        .level-name {
            font-size: 1.5rem;
            font-weight: 700;
            margin-bottom: 0.5rem;
            color: var(--text-primary);
        }

        .level-description {
            color: var(--text-secondary);
            font-size: 0.9rem;
            line-height: 1.6;
            margin-bottom: 1rem;
        }

        .level-topics {
            font-size: 0.85rem;
            color: var(--text-secondary);
            font-style: italic;
        }

        .back-button {
            display: inline-block;
            margin-bottom: 2rem;
            padding: 0.75rem 1.5rem;
            background: var(--bg-card);
            color: var(--text-primary);
            text-decoration: none;
            border-radius: 8px;
            transition: all 0.3s;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .back-button:hover {
            background: #334155;
            transform: translateX(-5px);
        }

        @media (max-width: 768px) {
            h1 {
                font-size: 2rem;
            }

            .language-title {
                font-size: 1.5rem;
            }

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