@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@300;400;500;700&display=swap');
        
        :root {
            --primary-color: #003366; /* 深海蓝 */
            --secondary-color: #0066cc; /* 科技蓝 */
            --accent-color: #ff9900; /* 警示/强调橙 */
            --text-dark: #333333;
            --text-light: #666666;
            --bg-light: #f4f7f9;
            --white: #ffffff;
            --shadow: 0 4px 12px rgba(0,0,0,0.08);
            --transition: all 0.3s ease;
        }

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

        body {
            font-family: 'Noto Sans SC', sans-serif;
            line-height: 1.6;
            color: var(--text-dark);
            background-color: var(--bg-light);
        }

        a { text-decoration: none; color: inherit; }
        ul { list-style: none; }

        /* --- Header --- */
        header {
            background: var(--white);
            box-shadow: 0 2px 10px rgba(0,0,0,0.05);
            position: fixed;
            width: 100%;
            top: 0;
            z-index: 1000;
        }

        .nav-container {
            max-width: 1200px;
            margin: 0 auto;
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 1rem 2rem;
        }

        .logo {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--primary-color);
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .logo i { color: var(--secondary-color); }

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

        .nav-links a {
            font-weight: 500;
            color: var(--text-dark);
            transition: var(--transition);
        }

        .nav-links a:hover { color: var(--secondary-color); }
        .nav-links a.active { color: var(--secondary-color); border-bottom: 2px solid var(--secondary-color); }

        .search-bar {
            background: #eee;
            border-radius: 20px;
            padding: 5px 15px;
            display: flex;
            align-items: center;
        }
        .search-bar input {
            border: none;
            background: transparent;
            outline: none;
            padding: 5px;
        }

        /* --- Hero Section --- */
        .hero {
            margin-top: 70px;
            height: 600px;
            background: linear-gradient(rgba(0, 51, 102, 0.8), rgba(0, 51, 102, 0.7)), 
                        url('https://images.unsplash.com/photo-1494412574643-35d324698420?ixlib=rb-4.0.3&auto=format&fit=crop&w=1920&q=80');
            background-size: cover;
            background-position: center;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            text-align: center;
            color: var(--white);
            padding: 0 20px;
        }

        .hero h1 {
            font-size: 3rem;
            margin-bottom: 1rem;
            font-weight: 700;
            text-shadow: 0 2px 4px rgba(0,0,0,0.3);
        }

        .hero p {
            font-size: 1.2rem;
            max-width: 700px;
            margin-bottom: 2.5rem;
            opacity: 0.9;
        }

        .hero-btns {
            display: flex;
            gap: 20px;
        }

        .btn {
            padding: 12px 30px;
            border-radius: 5px;
            font-weight: 600;
            transition: var(--transition);
            cursor: pointer;
        }

        .btn-primary {
            background: var(--secondary-color);
            color: var(--white);
            border: 2px solid var(--secondary-color);
        }

        .btn-primary:hover {
            background: #0055aa;
            border-color: #0055aa;
        }

        .btn-outline {
            background: transparent;
            color: var(--white);
            border: 2px solid var(--white);
        }

        .btn-outline:hover {
            background: var(--white);
            color: var(--primary-color);
        }

        /* --- Features Cards (The 3 Pillars) --- */
        .pillars {
            max-width: 1200px;
            margin: -60px auto 60px; /* Overlap hero */
            position: relative;
            z-index: 10;
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 30px;
            padding: 0 20px;
        }

        .pillar-card {
            background: var(--white);
            padding: 30px;
            border-radius: 8px;
            box-shadow: var(--shadow);
            transition: var(--transition);
            border-top: 4px solid transparent;
        }

        .pillar-card:hover {
            transform: translateY(-10px);
            box-shadow: 0 10px 20px rgba(0,0,0,0.1);
        }

        .pillar-card.shipping { border-top-color: #00a8cc; }
        .pillar-card.customs { border-top-color: #e91e63; }
        .pillar-card.trade { border-top-color: #ff9900; }

        .icon-box {
            width: 60px;
            height: 60px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            margin-bottom: 20px;
            font-size: 1.5rem;
        }

        .shipping .icon-box { background: rgba(0, 168, 204, 0.1); color: #00a8cc; }
        .customs .icon-box { background: rgba(233, 30, 99, 0.1); color: #e91e63; }
        .trade .icon-box { background: rgba(255, 153, 0, 0.1); color: #ff9900; }

        .pillar-card h3 { margin-bottom: 15px; font-size: 1.4rem; }
        .pillar-card p { color: var(--text-light); font-size: 0.95rem; margin-bottom: 20px; }
        
        .pillar-link {
            color: var(--secondary-color);
            font-weight: 600;
            font-size: 0.9rem;
            display: inline-flex;
            align-items: center;
            gap: 5px;
        }

        /* --- Detailed Knowledge System (Tabs) --- */
        .knowledge-system {
            max-width: 1200px;
            margin: 0 auto 80px;
            padding: 0 20px;
        }

        .section-header {
            text-align: center;
            margin-bottom: 40px;
        }
        .section-header h2 { font-size: 2rem; color: var(--primary-color); margin-bottom: 10px; }
        .section-header p { color: var(--text-light); }

        /* Tabs */
        .tabs {
            display: flex;
            justify-content: center;
            gap: 20px;
            margin-bottom: 40px;
        }

        .tab-btn {
            padding: 10px 30px;
            border: none;
            background: #e0e0e0;
            border-radius: 30px;
            font-size: 1rem;
            font-weight: 600;
            color: var(--text-light);
            cursor: pointer;
            transition: var(--transition);
        }

        .tab-btn.active {
            background: var(--primary-color);
            color: var(--white);
            box-shadow: 0 4px 10px rgba(0, 51, 102, 0.3);
        }

        /* Grid Content */
        .grid-content {
            display: none; /* Hidden by default */
            grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
            gap: 25px;
            animation: fadeIn 0.5s ease;
        }

        .grid-content.active { display: grid; }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .knowledge-item {
            background: var(--white);
            border: 1px solid #eee;
            border-radius: 8px;
            overflow: hidden;
        }

        .k-header {
            background: #f8f9fa;
            padding: 15px 20px;
            font-weight: 700;
            color: var(--primary-color);
            border-bottom: 1px solid #eee;
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .k-body { padding: 20px; }
        .k-body ul { list-style: none; }
        .k-body li {
            position: relative;
            padding-left: 20px;
            margin-bottom: 10px;
            color: var(--text-light);
            font-size: 0.9rem;
        }
        .k-body li::before {
            content: "•";
            color: var(--secondary-color);
            position: absolute;
            left: 0;
            font-weight: bold;
        }

        /* --- Footer --- */
        footer {
            background: var(--primary-color);
            color: #ccc;
            padding: 60px 0 20px;
        }

        .footer-content {
            max-width: 1200px;
            margin: 0 auto;
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 40px;
            padding: 0 20px;
            margin-bottom: 40px;
        }

        .footer-col h4 {
            color: var(--white);
            margin-bottom: 20px;
            font-size: 1.1rem;
        }

        .footer-col ul li { margin-bottom: 10px; }
        .footer-col ul li a:hover { color: var(--white); }

        .copyright {
            text-align: center;
            border-top: 1px solid rgba(255,255,255,0.1);
            padding-top: 20px;
            font-size: 0.85rem;
        }

        /* Mobile Responsive */
        @media (max-width: 768px) {
            .hero h1 { font-size: 2rem; }
            .tabs { flex-wrap: wrap; gap: 10px; }
            .nav-links { display: none; } /* Simplified for demo */
        }