/* --- 1. SETUP & VARS --- */
        :root {
            --bg-body: #0b1121;
            --bg-card: rgba(30, 41, 59, 0.6);
            --bg-glass: rgba(255, 255, 255, 0.03);
            --primary: #6366f1; /* Indigo */
            --accent: #ec4899;  /* Pink */
            --ai-color: #eab308; /* Yellow for AI */
            --mmo-color: #0ea5e9; /* Sky Blue for MMO */
            --student-color: #f43f5e; /* Rose for Student */
            --util-color: #22c55e; /* Green for Util */
            
            --text-main: #f8fafc;
            --text-muted: #94a3b8;
            --gradient-text: linear-gradient(to right, #2dd4bf, #38bdf8);
            --border-glass: 1px solid rgba(255, 255, 255, 0.08);
        }

        * { margin: 0; padding: 0; box-sizing: border-box; scroll-behavior: smooth; }
        
        body {
            font-family: 'Inter', sans-serif;
            background-color: var(--bg-body);
            color: var(--text-main);
            line-height: 1.6;
            overflow-x: hidden;
            background-image: radial-gradient(circle at 10% 20%, rgba(99, 102, 241, 0.08), transparent 20%),
                              radial-gradient(circle at 90% 80%, rgba(236, 72, 153, 0.08), transparent 20%);
        }

        a { text-decoration: none; color: inherit; transition: 0.3s; }
        ul { list-style: none; }
        h1, h2, h3, .logo { font-family: 'Outfit', sans-serif; }
        .container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
        
        /* Tiện ích Text */
        .text-gradient { background: var(--gradient-text); -webkit-background-clip: text; -webkit-text-fill-color: transparent; }
        .section-title { text-align: center; margin-bottom: 50px; margin-top: 80px; }
        .section-title h2 { font-size: 2.5rem; margin-bottom: 10px; }
        .section-title p { color: var(--text-muted); font-size: 1.1rem; }

        /* --- 2. HEADER --- */
        header {
            position: sticky; top: 0; z-index: 1000;
            background: rgba(11, 17, 33, 0.9); backdrop-filter: blur(12px);
            border-bottom: var(--border-glass); padding: 15px 0;
        }
        header .container { display: flex; justify-content: space-between; align-items: center; }
        .logo { font-size: 1.6rem; font-weight: 800; letter-spacing: -0.5px; }
        .logo span { color: var(--primary); }

        .desktop-nav ul { display: flex; gap: 30px; }
        .desktop-nav a:hover { color: var(--primary); }
        
        /* Sidebar Mobile */
        .hamburger { display: none; font-size: 1.5rem; cursor: pointer; }
        .mobile-sidebar {
            position: fixed; top: 0; left: -300px; width: 280px; height: 100vh;
            background: #0f172a; z-index: 2000; padding: 25px;
            transition: left 0.3s ease; border-right: var(--border-glass);
        }
        .mobile-sidebar.active { left: 0; }
        .overlay {
            position: fixed; top: 0; left: 0; width: 100%; height: 100%;
            background: rgba(0,0,0,0.8); z-index: 1500;
            opacity: 0; visibility: hidden; transition: 0.3s;
        }
        .overlay.active { opacity: 1; visibility: visible; }
        .sidebar-nav a { display: block; padding: 12px 0; border-bottom: var(--border-glass); font-size: 1.1rem; }

        /* --- 3. HERO --- */
        .hero { padding: 80px 0 40px; text-align: center; }
        .hero h1 { font-size: 3.5rem; line-height: 1.2; margin-bottom: 20px; }
        .hero p { color: var(--text-muted); font-size: 1.2rem; margin-bottom: 40px; max-width: 600px; margin-left: auto; margin-right: auto; }
        
        .search-box { position: relative; max-width: 500px; margin: 0 auto 50px; }
        .search-box input {
            width: 100%; padding: 18px 25px; padding-right: 50px;
            border-radius: 50px; border: var(--border-glass);
            background: var(--bg-glass); color: #fff; font-size: 1rem; outline: none;
        }
        .search-box input:focus { border-color: var(--primary); background: rgba(255,255,255,0.1); }
        .search-box i { position: absolute; right: 20px; top: 50%; transform: translateY(-50%); color: var(--text-muted); }

        /* Stats Bar */
        .stats-bar {
            display: flex; justify-content: center; gap: 60px; flex-wrap: wrap;
            padding: 30px; background: var(--bg-glass); border-radius: 20px;
            border: var(--border-glass); margin-bottom: 60px;
        }
        .stat-item { text-align: center; }
        .stat-item h3 { font-size: 2rem; color: var(--primary); margin-bottom: 5px; }
        .stat-item span { color: var(--text-muted); font-size: 0.85rem; text-transform: uppercase; letter-spacing: 1px; }

        /* --- 4. TOOLS SECTION --- */
        .category-tabs { display: flex; justify-content: center; gap: 15px; margin-bottom: 40px; flex-wrap: wrap; }
        .tab-btn {
            padding: 10px 25px; border-radius: 30px; border: var(--border-glass);
            background: transparent; color: var(--text-muted); cursor: pointer; font-weight: 600; transition: 0.3s;
        }
        .tab-btn:hover, .tab-btn.active { background: var(--primary); color: #fff; border-color: var(--primary); box-shadow: 0 0 15px rgba(99, 102, 241, 0.4); }

        .tools-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 25px; }
        .tool-card {
            background: var(--bg-card); border: var(--border-glass);
            border-radius: 20px; padding: 25px; position: relative;
            transition: 0.3s; cursor: pointer; overflow: hidden;
        }
        .tool-card:hover { transform: translateY(-5px); border-color: rgba(255,255,255,0.2); }
        .card-icon { width: 50px; height: 50px; border-radius: 12px; display: flex; align-items: center; justify-content: center; font-size: 1.5rem; margin-bottom: 15px; }
        
        /* Specific Category Colors */
        .icon-ai { background: rgba(234, 179, 8, 0.15); color: var(--ai-color); }
        .icon-student { background: rgba(244, 63, 94, 0.15); color: var(--student-color); }
        .icon-mmo { background: rgba(14, 165, 233, 0.15); color: var(--mmo-color); }
        .icon-util { background: rgba(34, 197, 94, 0.15); color: var(--util-color); }
        
        .tag { position: absolute; top: 15px; right: 15px; font-size: 0.7rem; padding: 4px 10px; border-radius: 20px; background: rgba(255,255,255,0.05); }

        /* --- 5. FEATURES (Moved Down) --- */
        .features-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 30px; margin-top: 30px; }
        .feature-box {
            padding: 30px; background: var(--bg-glass); border-radius: 20px; border: var(--border-glass); text-align: center;
        }
        .feature-box i { font-size: 2.5rem; color: var(--accent); margin-bottom: 20px; }

        /* --- 6. ABOUT & FAQ (Moved Down) --- */
        .about-section {
            display: flex; align-items: center; gap: 50px; padding: 50px;
            background: linear-gradient(to right, rgba(30,41,59,0.5), rgba(15,23,42,0));
            border-radius: 30px; border: var(--border-glass);
        }
        .about-text { flex: 1; }
        .about-image { flex: 1; height: 250px; background: rgba(255,255,255,0.03); border-radius: 20px; display: flex; align-items: center; justify-content: center; font-size: 4rem; color: var(--text-muted); }

        .faq-item {
            background: var(--bg-glass); border: var(--border-glass); margin-bottom: 15px; border-radius: 10px; overflow: hidden;
        }
        .faq-question { padding: 20px; cursor: pointer; display: flex; justify-content: space-between; font-weight: 600; }
        .faq-answer { padding: 0 20px 20px; color: var(--text-muted); display: none; line-height: 1.6; }
        .faq-item.active .faq-answer { display: block; }
        .faq-item.active .faq-question { color: var(--primary); }

        /* --- 7. FOOTER --- */
        .newsletter { text-align: center; padding: 60px 20px; background: radial-gradient(circle, rgba(99,102,241,0.15) 0%, rgba(11,17,33,0) 70%); }
        .newsletter-form { display: flex; max-width: 400px; margin: 30px auto 0; gap: 10px; }
        .newsletter-form input { flex: 1; padding: 12px 20px; border-radius: 50px; border: none; outline: none; }
        .newsletter-form button { padding: 12px 30px; border-radius: 50px; border: none; background: var(--primary); color: #fff; font-weight: bold; cursor: pointer; }

        footer { background: #020617; padding: 60px 0 30px; border-top: var(--border-glass); }
        .footer-grid { display: grid; grid-template-columns: 1.5fr 1fr 1fr 1fr; gap: 40px; margin-bottom: 40px; }
        .social-links { display: flex; gap: 15px; margin-top: 20px; }
        .social-links a { width: 40px; height: 40px; background: rgba(255,255,255,0.1); display: flex; align-items: center; justify-content: center; border-radius: 50%; }
        
        /* Responsive */
        @media (max-width: 768px) {
            .desktop-nav { display: none; }
            .hamburger { display: block; }
            .hero h1 { font-size: 2.5rem; }
            .features-grid, .about-section, .footer-grid { grid-template-columns: 1fr; text-align: center; }
            .about-section { flex-direction: column; padding: 30px; gap: 30px; }
            .newsletter-form { flex-direction: column; }
            .stats-bar { gap: 30px; }
        }