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

        body {
            font-family: 'Inter', system-ui, -apple-system, 'Segoe UI', sans-serif;
            background: #F8FAFE;
            color: #121826;
        }

        .header {
            background: rgba(255, 255, 255, 0.96);
            backdrop-filter: blur(12px);
            border-bottom: 1px solid #E9EDF4;
            position: sticky;
            top: 0;
            z-index: 50;
        }

        .nav-container {
            max-width: 1360px;
            margin: 0 auto;
            padding: 1rem 2rem;
            display: flex;
            align-items: center;
            justify-content: space-between;
            flex-wrap: wrap;
        }

        .logo {
            font-size: 1.9rem;
            font-weight: 800;
            background: linear-gradient(110deg, #1F2B4E, #2666C9);
            background-clip: text;
            -webkit-background-clip: text;
            color: transparent;
            letter-spacing: -0.02em;
        }

        .nav-links {
            display: flex;
            gap: 2rem;
        }

        .nav-links a {
            text-decoration: none;
            font-weight: 500;
            color: #2D3A5E;
            transition: 0.2s;
        }

        .nav-links a.active, .nav-links a:hover {
            color: #2666C9;
        }

        .guide-wrapper {
            max-width: 1360px;
            margin: 2rem auto 4rem;
            padding: 0 2rem;
            display: flex;
            flex-wrap: wrap;
            gap: 2.5rem;
        }

        .sidebar {
            flex: 0.9;
            background: #FFFFFF;
            border-radius: 2rem;
            padding: 1.8rem;
            height: fit-content;
            position: sticky;
            top: 90px;
            border: 1px solid #EDF2F7;
            box-shadow: 0 8px 20px rgba(0,0,0,0.02);
        }

        .sidebar h3 {
            margin-bottom: 1rem;
            font-weight: 700;
            font-size: 1.2rem;
        }

        .topic-list {
            list-style: none;
        }

        .topic-list li {
            margin: 0.6rem 0;
            padding: 0.7rem 1rem;
            border-radius: 1rem;
            cursor: pointer;
            transition: all 0.2s;
            font-weight: 500;
            color: #2C3E68;
            display: flex;
            align-items: center;
            gap: 0.6rem;
        }

        .topic-list li:hover {
            background: #F0F4FE;
        }

        .topic-list li.active-topic {
            background: #EFF4FF;
            color: #2666C9;
            border-left: 3px solid #2666C9;
        }

        .main-content {
            flex: 2.5;
        }

        .topic-content {
            display: none;
            animation: fadeIn 0.3s ease;
        }

        .topic-content.active-content {
            display: block;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(8px);}
            to { opacity: 1; transform: translateY(0);}
        }

        .guide-hero-card {
            background: linear-gradient(135deg, #1E2A4A 0%, #14203E 100%);
            border-radius: 2rem;
            padding: 2rem;
            margin-bottom: 2rem;
            color: white;
        }

        .guide-hero-card h2 {
            font-size: 1.9rem;
            font-weight: 700;
            margin-bottom: 0.5rem;
        }

        .guide-hero-card p {
            opacity: 0.85;
            margin-bottom: 1.2rem;
        }

        .stat-row {
            display: flex;
            gap: 1.5rem;
            margin-top: 1rem;
        }

        .stat-badge {
            background: rgba(255,255,255,0.15);
            border-radius: 40px;
            padding: 0.3rem 1rem;
            font-size: 0.8rem;
        }

        .lesson-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
            gap: 1.5rem;
            margin: 1.5rem 0;
        }

        .lesson-card {
            background: white;
            border-radius: 1.5rem;
            padding: 1.5rem;
            border: 1px solid #EFF3F8;
            transition: all 0.2s;
            box-shadow: 0 2px 8px rgba(0,0,0,0.02);
        }

        .lesson-card:hover {
            transform: translateY(-4px);
            box-shadow: 0 20px 30px -12px rgba(0,0,0,0.1);
            border-color: #D6E4FF;
        }

        .lesson-icon {
            font-size: 2rem;
            margin-bottom: 0.8rem;
        }

        .lesson-card h3 {
            font-size: 1.3rem;
            margin-bottom: 0.5rem;
        }

        .meta-info {
            display: flex;
            gap: 1rem;
            margin: 1rem 0;
            font-size: 0.8rem;
            color: #6C7A95;
        }

        .btn-guide {
            background: #F0F4FE;
            color: #2666C9;
            border: none;
            border-radius: 40px;
            padding: 0.5rem 1.2rem;
            font-weight: 600;
            font-size: 0.85rem;
            cursor: pointer;
            text-decoration: none;
            display: inline-block;
            transition: 0.2s;
        }

        .btn-guide:hover {
            background: #2666C9;
            color: white;
        }

        .code-block {
            background: #1E293B;
            border-radius: 1rem;
            padding: 1rem;
            margin: 1rem 0;
            font-family: monospace;
            font-size: 0.8rem;
            color: #A5F3C3;
            overflow-x: auto;
        }

        .feature-list {
            list-style: none;
            margin: 1rem 0;
        }

        .feature-list li {
            padding: 0.5rem 0;
            display: flex;
            align-items: center;
            gap: 0.6rem;
            border-bottom: 1px solid #F0F4FA;
        }

        .resource-banner {
            background: linear-gradient(115deg, #F2F6FD, #FFFFFF);
            border-radius: 1.5rem;
            padding: 1.5rem;
            margin-top: 1.5rem;
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            align-items: center;
            border: 1px solid #E9EDF4;
        }

        .footer {
            background: #F9F9FE;
            border-top: 1px solid #E9EDF4;
            margin-top: 2rem;
        }

        .footer-container {
            max-width: 1280px;
            margin: 0 auto;
            padding: 3rem 2rem 2rem;
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
        }

        .footer-col a {
            display: block;
            color: #5C6885;
            text-decoration: none;
            margin-bottom: 0.5rem;
            font-size: 0.9rem;
        }

        .copyright {
            text-align: center;
            padding: 1.5rem;
            font-size: 0.8rem;
            color: #6C7A95;
            border-top: 1px solid #E9EDF4;
        }

        @media (max-width: 850px) {
            .sidebar { position: static; }
            .guide-wrapper { flex-direction: column; }
        }