:root {
            --primary: #004e9a;
            --accent: #e74c3c;
            --bg: #f8f9fa;
            --text: #333;
            --white: #fff;
        }

        /* [NEW] Chặn hành vi chọn văn bản, zoom, kéo nảy trên mobile */
        html,
        body {
            -webkit-user-select: none;
            -moz-user-select: none;
            -ms-user-select: none;
            user-select: none;
            touch-action: pan-x pan-y;
            overscroll-behavior: none;
        }

        body {
            font-family: 'Montserrat', sans-serif;
            background: var(--bg);
            color: var(--text);
            margin: 0;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
        }

        .container {
            max-width: 800px;
            margin: 0 auto;
            padding: 40px 20px;
            flex: 1;
            width: 100%;
            box-sizing: border-box;
        }

        /* Cho phép chọn văn bản trong ô input để copy */
        input {
            -webkit-user-select: auto;
            -moz-user-select: auto;
            -ms-user-select: auto;
            user-select: auto;
        }

        /* HEADER */
        .header-box {
            text-align: center;
            margin-bottom: 40px;
        }

        .header-box h1 {
            color: var(--primary);
            font-weight: 800;
            font-size: 2rem;
            margin-bottom: 10px;
        }

        .header-box p {
            color: #666;
            font-size: 1rem;
        }

        /* COPY SECTION */
        .copy-section {
            background: white;
            padding: 25px;
            border-radius: 15px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
            margin-bottom: 30px;
            border: 2px solid #eef2f5;
        }

        .copy-label {
            font-weight: 700;
            color: var(--primary);
            margin-bottom: 10px;
            display: block;
        }

        .copy-box {
            display: flex;
            gap: 10px;
            flex-wrap: wrap;
        }

        .copy-input {
            flex: 1;
            padding: 12px 15px;
            border: 1px solid #ddd;
            border-radius: 8px;
            background: #f9f9f9;
            font-family: monospace;
            font-size: 0.95rem;
            color: #333;
        }

        .btn-copy {
            background: var(--primary);
            color: white;
            border: none;
            padding: 0 25px;
            border-radius: 8px;
            font-weight: 600;
            cursor: pointer;
            transition: 0.3s;
            white-space: nowrap;
            height: 45px;
        }

        .btn-copy:active {
            transform: scale(0.95);
        }

        .btn-copy.copied {
            background: #27ae60;
        }

        /* CONTACT GRID */
        .contact-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 20px;
        }

        .contact-card {
            background: white;
            padding: 20px;
            border-radius: 12px;
            display: flex;
            align-items: center;
            gap: 15px;
            box-shadow: 0 3px 10px rgba(0, 0, 0, 0.05);
            transition: 0.3s;
            cursor: pointer;
            text-decoration: none;
            color: inherit;
            border: 1px solid transparent;
        }

        .contact-card:hover {
            transform: translateY(-5px);
            border-color: var(--primary);
            box-shadow: 0 8px 20px rgba(0, 0, 0, 0.1);
        }

        .icon-box {
            width: 50px;
            height: 50px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1.5rem;
            color: white;
            flex-shrink: 0;
        }

        .zalo-bg {
            background: #0068ff;
        }

        .fb-bg {
            background: #1877f2;
        }

        .page-bg {
            background: linear-gradient(45deg, #1877f2, #0099ff);
        }

        .group-bg {
            background: #00a400;
        }

        .info-box h3 {
            margin: 0;
            font-size: 1rem;
            font-weight: 700;
            color: #333;
        }

        .info-box span {
            font-size: 0.85rem;
            color: #666;
        }

        /* BACK BUTTON */
        .back-nav {
            margin-bottom: 20px;
        }

        .btn-back {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            color: #666;
            font-weight: 600;
            cursor: pointer;
            transition: 0.3s;
            text-decoration: none;
        }

        .btn-back:hover {
            color: var(--primary);
            transform: translateX(-5px);
        }

        footer {
            text-align: center;
            padding: 20px;
            color: #999;
            font-size: 0.85rem;
            margin-top: auto;
        }

        @media(max-width: 600px) {
            .header-box h1 {
                font-size: 1.5rem;
            }

            .copy-box {
                flex-direction: column;
            }

            .btn-copy {
                width: 100%;
            }
        }