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

        :root {
            --primary: #8b5cf6;
            --primary-dark: #7c3aed;
            --secondary: #10b981;
            --bg-primary: #ffffff;
            --bg-secondary: #f8fafc;
            --bg-card: #ffffff;
            --text-primary: #1f2937;
            --text-secondary: #6b7280;
            --border: #e5e7eb;
            --shadow: rgba(0, 0, 0, 0.1);
            --shadow-lg: rgba(0, 0, 0, 0.15);
            --accent: #8b5cf6;
            --navbar-bg: #ffffff;
            --code-bg: #f1f5f9;
            --success: #10b981;
            --info: #3b82f6;
            --warning: #f59e0b;
        }

        [data-theme="dark"] {
            --bg-primary: #111827;
            --bg-secondary: #1f2937;
            --bg-card: #1f2937;
            --text-primary: #f9fafb;
            --text-secondary: #d1d5db;
            --border: #374151;
            --shadow: rgba(0, 0, 0, 0.3);
            --shadow-lg: rgba(0, 0, 0, 0.5);
            --navbar-bg: #111827;
            --code-bg: #0f172a;
        }

        body {
            font-family: 'Inter', sans-serif;
            background: var(--bg-primary);
            color: var(--text-primary);
            line-height: 1.6;
            transition: background-color 0.3s ease, color 0.3s ease;
        }


        /* Hero Section */
        .hero {
            text-align: center;
            padding: 4rem 2rem;
            background: linear-gradient(135deg, rgba(139, 92, 246, 0.1), rgba(16, 185, 129, 0.1));
            border-bottom: 2px solid var(--border);
        }

        .hero h1 {
            font-size: 3rem;
            margin-bottom: 1rem;
            background: linear-gradient(135deg, var(--primary), var(--secondary));
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
        }

        .hero p {
            font-size: 1.25rem;
            color: var(--text-secondary);
            max-width: 700px;
            margin: 0 auto;
        }

        /* Content Container */
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 3rem 2rem;
        }

        /* Filter Section */
        .filter-section {
            margin-bottom: 3rem;
            text-align: center;
        }

        .filter-buttons {
            display: flex;
            flex-wrap: wrap;
            gap: 1rem;
            justify-content: center;
            margin-top: 1.5rem;
        }

        .filter-btn {
            padding: 12px 24px;
            border: 2px solid var(--border);
            background: var(--bg-card);
            color: var(--text-primary);
            border-radius: 50px;
            cursor: pointer;
            font-weight: 600;
            font-size: 0.95rem;
            transition: all 0.3s ease;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .filter-btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px var(--shadow);
            border: 1px solid goldenrod;
        }

        .filter-btn.active {
            background: linear-gradient(135deg, var(--primary), var(--secondary));
            color: white;
            border-color: goldenrod;
        }

        /* Questions Grid */
        .questions-grid {
            display: grid;
            gap: 2rem;
        }

        .question-card {
            background: var(--bg-card);
            border: 2px solid var(--border);
            border-radius: 16px;
            overflow: hidden;
            transition: all 0.3s ease;
        }

        .question-card:hover {
            box-shadow: 0 8px 24px var(--shadow-lg);
            transform: translateY(-4px);
            border-color: var(--primary);
        }

        .question-header {
            padding: 1.5rem;
            cursor: pointer;
            display: flex;
            justify-content: space-between;
            align-items: flex-start;
            gap: 1rem;
            transition: background 0.3s ease;
        }

        .question-header:hover {
            background: var(--bg-secondary);
        }

        .question-left {
            flex: 1;
        }

        .question-number {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            width: 32px;
            height: 32px;
            background: linear-gradient(135deg, var(--primary), var(--secondary));
            color: white;
            border-radius: 12px;
            font-weight: 700;
            font-size: 0.9rem;
            margin-bottom: 1rem;
            box-shadow: 0 4px 12px var(--shadow);
            transition: all 0.3s ease;
        }

        .question-number:hover {
            transform: scale(1.05);
        }

        .difficulty-badge {
            display: inline-block;
            padding: 4px 12px;
            border-radius: 20px;
            font-size: 0.75rem;
            font-weight: 600;
            margin-bottom: 0.5rem;
        }

        .difficulty-beginner {
            background: rgba(16, 185, 129, 0.2);
            color: var(--secondary);
        }

        .difficulty-intermediate {
            background: rgba(59, 130, 246, 0.2);
            color: var(--info);
        }

        .difficulty-advanced {
            background: rgba(245, 158, 11, 0.2);
            color: var(--warning);
        }

        .difficulty-expert {
            background: rgba(239, 68, 68, 0.2);
            color: #ef4444;
        }

        .question-title {
            font-size: 1.2rem;
            font-weight: 600;
            color: var(--text-primary);
            margin-bottom: 0.5rem;
        }

        .question-meta {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
            font-size: 0.85rem;
            color: var(--text-secondary);
        }

        .meta-item {
            display: flex;
            align-items: center;
            gap: 0.3rem;
        }

        .expand-icon {
            font-size: 1.5rem;
            color: var(--primary);
            transition: transform 0.3s ease;
        }

        .question-card.expanded .expand-icon {
            transform: rotate(180deg);
        }

        .question-answer {
            max-height: 0;
            overflow: hidden;
            transition: max-height 0.4s ease;
        }

        .question-card.expanded .question-answer {
            max-height: 3000px;
        }

        .answer-content {
            padding: 0 1.5rem 1.5rem;
            border-top: 2px solid var(--border);
        }

        .answer-text {
            color: var(--text-secondary);
            line-height: 1.8;
            margin-bottom: 1rem;
        }

        .code-block {
            background: var(--code-bg);
            border: 1px solid var(--border);
            border-radius: 8px;
            padding: 1rem;
            margin: 1rem 0;
            overflow-x: auto;
            position: relative;
        }

        .code-block pre {
            margin: 0;
            font-family: 'Courier New', monospace;
            font-size: 0.9rem;
            color: var(--text-primary);
            line-height: 1.6;
        }

        .code-label {
            font-size: 0.75rem;
            font-weight: 600;
            color: var(--primary);
            margin-bottom: 0.5rem;
            display: inline-block;
        }

        .key-points {
            background: linear-gradient(135deg, rgba(139, 92, 246, 0.1), rgba(16, 185, 129, 0.1));
            border-left: 4px solid var(--primary);
            padding: 1rem;
            margin: 1rem 0;
            border-radius: 8px;
        }

        .key-points h4 {
            color: var(--primary);
            margin-bottom: 0.5rem;
            font-size: 1rem;
        }

        .key-points ul {
            margin-left: 1.5rem;
            color: var(--text-secondary);
        }

        .key-points li {
            margin-bottom: 0.3rem;
        }

        /* Responsive Design */
        @media (max-width: 768px) {
            .hero h1 {
                font-size: 2rem;
            }

            .filter-buttons {
                flex-direction: column;
                align-items: stretch;
            }

            .filter-btn {
                justify-content: center;
            }

            .question-title {
                font-size: 1rem;
            }
        }

        /* Animation for filter */
        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }