/* ========= CSS Variables ========= */
        :root {
            --primary: #2563eb;
            --primary-dark: #1d4ed8;
            --secondary: #7c3aed;
            --accent: #06b6d4;
            --dark: #0f172a;
            --light: #f8fafc;
            --gray-light: #e2e8f0;
            --gray: #94a3b8;
            --gray-dark: #475569;
            --success: #10b981;
            --warning: #f59e0b;
            --danger: #ef4444;

            --radius-sm: 6px;
            --radius-md: 12px;
            --radius-lg: 20px;
            --radius-xl: 30px;

            --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.05);
            --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.08);
            --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.1);
            --shadow-xl: 0 20px 60px rgba(0, 0, 0, 0.12);

            --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
            --transition-fast: all 0.15s ease;
        }

        /* ========= General Reset & Layout ========= */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        html {
            scroll-behavior: smooth;
        }

        body {
            font-family: 'Inter', sans-serif;
            color: var(--dark);
            background-color: var(--light);
            line-height: 1.7;
            font-weight: 400;
            overflow-x: hidden;
        }

        h1, h2, h3, h4, h5 {
            font-weight: 700;
            line-height: 1.2;
            margin-bottom: 1rem;
        }

        h1 {
            font-size: 3.5rem;
            font-weight: 800;
            background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
            -webkit-background-clip: text;
            background-clip: text;
            color: transparent;
            letter-spacing: -0.02em;
        }

        h2 {
            font-size: 2.5rem;
            margin-bottom: 2rem;
            position: relative;
            display: inline-block;
        }

        h2:after {
            content: '';
            position: absolute;
            bottom: -8px;
            left: 0;
            width: 60px;
            height: 4px;
            background: linear-gradient(90deg, var(--primary), var(--accent));
            border-radius: 2px;
        }

        h3 {
            font-size: 1.5rem;
            color: var(--dark);
        }

        p {
            margin-bottom: 1.5rem;
            font-size: 1.1rem;
            color: var(--gray-dark);
        }

        a {
            text-decoration: none;
            color: var(--primary);
            transition: var(--transition-fast);
        }

        a:hover {
            color: var(--primary-dark);
        }

        strong {
            font-weight: 600;
            color: var(--dark);
        }

        ul, ol {
            padding-left: 1.5rem;
            margin-bottom: 1.5rem;
        }

        li {
            margin-bottom: 0.5rem;
            color: var(--gray-dark);
        }

        section {
            padding: 5rem 0;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 2rem;
        }

        .section-header {
            text-align: center;
            margin-bottom: 3rem;
        }

        .section-header h2 {
            display: inline-block;
        }

        /* ========= Navigation ========= */
        .navbar {
            position: fixed;
            top: 0;
            left: 0;
            right: 0;
            background-color: rgba(255, 255, 255, 0.95);
            backdrop-filter: blur(10px);
            border-bottom: 1px solid rgba(0, 0, 0, 0.05);
            z-index: 1000;
            padding: 1rem 0;
            transition: var(--transition);
        }

        .navbar.scrolled {
            padding: 0.7rem 0;
            box-shadow: var(--shadow-md);
        }

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

        .logo {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--dark);
            display: flex;
            align-items: center;
            white-space: nowrap;
            flex-shrink: 0;
        }

        .logo-dot {
            color: var(--primary);
            font-size: 2rem;
            margin-right: 2px;
        }

        .nav-links {
            display: flex;
            gap: 1.8rem;
            align-items: center;
        }

        .nav-links a {
            color: var(--gray-dark);
            font-weight: 500;
            font-size: 0.95rem;
            position: relative;
            padding: 0.5rem 0;
        }

        .nav-links a:after {
            content: '';
            position: absolute;
            bottom: 0;
            left: 0;
            width: 0;
            height: 2px;
            background: linear-gradient(90deg, var(--primary), var(--accent));
            transition: var(--transition);
        }

        .nav-links a:hover {
            color: var(--dark);
        }

        .nav-links a:hover:after {
            width: 100%;
        }

        .nav-links a.active {
            color: var(--dark);
        }

        .nav-links a.active:after {
            width: 100%;
        }

        .nav-links a.nav-cta {
            background: linear-gradient(135deg, #0d9488, #2563eb);
            color: #fff;
            padding: 0.45rem 1.1rem;
            border-radius: 999px;
            white-space: nowrap;
            box-shadow: 0 2px 10px rgba(13, 148, 136, 0.3);
        }

        .nav-links a.nav-cta:hover {
            color: #fff;
            transform: translateY(-1px);
            box-shadow: 0 4px 14px rgba(13, 148, 136, 0.45);
        }

        .nav-links a.nav-cta:after {
            display: none;
        }

        .mobile-menu-btn {
            display: none;
            background: none;
            border: none;
            font-size: 1.5rem;
            cursor: pointer;
            color: var(--dark);
        }

        /* ========= Hero Section ========= */
        .hero {
            padding: 10rem 0 6rem;
            position: relative;
            overflow: hidden;
        }

        .hero:before {
            content: '';
            position: absolute;
            top: -50%;
            right: -20%;
            width: 70%;
            height: 150%;
            background: radial-gradient(circle, rgba(37, 99, 235, 0.05) 0%, rgba(124, 58, 237, 0.03) 70%, transparent 100%);
            border-radius: 50%;
            z-index: -1;
        }

        .hero:after {
            content: '';
            position: absolute;
            bottom: -30%;
            left: -10%;
            width: 60%;
            height: 100%;
            background: radial-gradient(circle, rgba(6, 182, 212, 0.05) 0%, rgba(124, 58, 237, 0.03) 70%, transparent 100%);
            border-radius: 50%;
            z-index: -1;
        }

        .hero-content {
            max-width: 900px;
            margin: 0 auto;
            text-align: center;
        }

        .hero h1 {
            margin-bottom: 1.5rem;
            font-size: 4rem;
        }

        .hero-subtitle {
            font-size: 1.5rem;
            font-weight: 600;
            color: var(--gray-dark);
            margin-bottom: 2rem;
            line-height: 1.4;
        }

        .authors {
            font-size: 1.1rem;
            color: var(--gray);
            margin-bottom: 2.5rem;
            line-height: 1.6;
        }

        .affiliation-cards {
            display: flex;
            justify-content: center;
            flex-wrap: wrap;
            gap: 1.5rem;
            margin: 2.5rem 0;
        }

        .affiliation-card {
            display: flex;
            flex-direction: column;
            align-items: center;
            padding: 1.5rem 1rem;
            background: white;
            border-radius: var(--radius-lg);
            box-shadow: var(--shadow-sm);
            transition: var(--transition);
            width: 150px;
        }

        .affiliation-card:hover {
            transform: translateY(-5px);
            box-shadow: var(--shadow-md);
        }

        .affiliation-image {
            width: 80px;
            height: 60px;
            object-fit: contain;
            margin-bottom: 0.8rem;
        }

        .affiliation {
            font-weight: 600;
            color: var(--dark);
            font-size: 0.9rem;
            text-align: center;
        }

        .hero-links {
            display: flex;
            justify-content: center;
            flex-wrap: wrap;
            gap: 1rem;
            margin-top: 3rem;
        }

        .btn {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            padding: 0.9rem 1.8rem;
            border-radius: var(--radius-md);
            font-weight: 600;
            font-size: 1rem;
            transition: var(--transition);
            border: none;
            cursor: pointer;
            gap: 0.5rem;
        }

        .btn-primary {
            background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
            color: white;
            box-shadow: 0 4px 14px rgba(37, 99, 235, 0.3);
        }

        .btn-primary:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(37, 99, 235, 0.4);
            color: white;
        }

        .btn-secondary {
            background: white;
            color: var(--dark);
            border: 1px solid var(--gray-light);
        }

        .btn-secondary:hover {
            transform: translateY(-2px);
            box-shadow: var(--shadow-md);
            color: var(--dark);
        }

        .btn-accent {
            background: linear-gradient(135deg, var(--accent) 0%, #0ea5e9 100%);
            color: white;
            box-shadow: 0 4px 14px rgba(6, 182, 212, 0.3);
        }

        .btn-accent:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(6, 182, 212, 0.4);
            color: white;
        }

        /* ========= Section Styles ========= */
        .section-light {
            background-color: white;
        }

        .section-gray {
            background-color: #f8fafc;
        }

        /* ========= Hardware Section ========= */
        .hardware-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
            gap: 1.5rem;
            margin: 2.5rem 0;
        }

        .hardware-item {
            background: white;
            padding: 1.5rem;
            border-radius: var(--radius-lg);
            box-shadow: var(--shadow-sm);
            transition: var(--transition);
            border-top: 4px solid var(--primary);
        }

        .hardware-item:hover {
            transform: translateY(-5px);
            box-shadow: var(--shadow-md);
        }

        .hardware-item h4 {
            color: var(--primary);
            margin-bottom: 0.5rem;
            font-size: 1.2rem;
        }

        /* ========= Media Components ========= */
        .media-container {
            margin: 2.5rem 0;
            border-radius: var(--radius-lg);
            overflow: hidden;
            box-shadow: var(--shadow-lg);
            text-align: center;
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 0;
        }

        .media-container img {
            width: 100%;
            height: auto;
            display: block;
        }

        /* ========= Benchmark Cards ========= */
        .benchmark-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
            gap: 2rem;
            margin: 3rem 0;
        }

        .benchmark-card {
            background: white;
            border-radius: var(--radius-lg);
            padding: 2rem;
            box-shadow: var(--shadow-md);
            transition: var(--transition);
            border-top: 6px solid;
            height: 100%;
        }

        .benchmark-card:hover {
            transform: translateY(-8px);
            box-shadow: var(--shadow-xl);
        }

        .benchmark-card.har {
            border-color: var(--primary);
        }

        .benchmark-card.hau {
            border-color: var(--success);
        }

        .benchmark-card.harn {
            border-color: var(--warning);
        }

        .benchmark-icon {
            font-size: 2.5rem;
            margin-bottom: 1.5rem;
        }

        /* ========= Dataset Modalities ========= */
        .modalities-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
            gap: 1.5rem;
            margin: 2.5rem 0;
        }

        .modality-card {
            background: white;
            padding: 1.5rem 1rem;
            border-radius: var(--radius-lg);
            box-shadow: var(--shadow-sm);
            text-align: center;
            transition: var(--transition);
        }

        .modality-card:hover {
            transform: translateY(-5px);
            box-shadow: var(--shadow-md);
        }

        .modality-icon {
            font-size: 2rem;
            margin-bottom: 1rem;
        }

        /* ========= Results Section ========= */
        .results-grid {
            display: grid;
            gap: 2rem;
            margin: 3rem 0;
        }

        .result-card {
            background: white;
            border-radius: var(--radius-lg);
            padding: 2rem;
            box-shadow: var(--shadow-md);
        }

        .result-card h4 {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            margin-bottom: 1.5rem;
        }

        .result-table {
            width: 100%;
            border-collapse: collapse;
        }

        .result-table th {
            text-align: left;
            padding: 0.8rem;
            background-color: #f1f5f9;
            font-weight: 600;
            color: var(--dark);
        }

        .result-table td {
            padding: 0.8rem;
            border-bottom: 1px solid var(--gray-light);
        }

        .result-table tr:last-child td {
            border-bottom: none;
        }

        /* ========= Citation ========= */
        .citation-box {
            background: white;
            border-radius: var(--radius-lg);
            padding: 2.5rem;
            box-shadow: var(--shadow-md);
            margin: 2rem 0;
            position: relative;
            border-left: 4px solid var(--primary);
        }

        .citation-box pre {
            background: #f8fafc;
            padding: 1.5rem;
            border-radius: var(--radius-md);
            overflow-x: auto;
            font-family: 'Courier New', monospace;
            font-size: 0.95rem;
            line-height: 1.5;
            color: var(--dark);
            border: 1px solid var(--gray-light);
        }

        /* ========= Footer ========= */
        footer {
            background: var(--dark);
            color: white;
            padding: 5rem 0 3rem;
        }

        .footer-content {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 3rem;
            margin-bottom: 3rem;
        }

        .footer-logo {
            font-size: 1.8rem;
            font-weight: 700;
            margin-bottom: 1rem;
        }

        .footer-links h4 {
            color: white;
            margin-bottom: 1.5rem;
            font-size: 1.2rem;
        }

        .footer-links ul {
            list-style: none;
            padding: 0;
        }

        .footer-links li {
            margin-bottom: 0.8rem;
        }

        .footer-links a {
            color: #cbd5e1;
            transition: var(--transition-fast);
        }

        .footer-links a:hover {
            color: white;
            padding-left: 5px;
        }

        .copyright {
            text-align: center;
            padding-top: 2rem;
            border-top: 1px solid #334155;
            color: #94a3b8;
            font-size: 0.9rem;
        }

        /* ========= Responsive Styles ========= */
        @media (max-width: 992px) {
            h1 {
                font-size: 3rem;
            }

            h2 {
                font-size: 2.2rem;
            }

            .hero {
                padding: 8rem 0 4rem;
            }
        }

        @media (max-width: 768px) {
            .mobile-menu-btn {
                display: block;
            }

            .nav-links {
                position: fixed;
                top: 70px;
                left: 0;
                right: 0;
                background: white;
                flex-direction: column;
                padding: 2rem;
                box-shadow: var(--shadow-lg);
                transform: translateY(-100%);
                opacity: 0;
                visibility: hidden;
                transition: var(--transition);
                z-index: 999;
            }

            .nav-links.active {
                transform: translateY(0);
                opacity: 1;
                visibility: visible;
            }

            .nav-links a {
                padding: 0.8rem 0;
                font-size: 1.1rem;
            }

            h1 {
                font-size: 2.5rem;
            }

            h2 {
                font-size: 2rem;
            }

            .hero-subtitle {
                font-size: 1.2rem;
            }

            .benchmark-grid,
            .results-grid {
                grid-template-columns: 1fr;
            }

            .hero-links {
                flex-direction: column;
                align-items: center;
            }

            .btn {
                width: 100%;
                max-width: 300px;
            }
        }

        @media (max-width: 480px) {
            .container {
                padding: 0 1.5rem;
            }

            h1 {
                font-size: 2rem;
            }

            h2 {
                font-size: 1.8rem;
            }

            section {
                padding: 3rem 0;
            }
        }

        /* ========= Animation Keyframes ========= */
        @keyframes fadeInUp {
            from {
                opacity: 0;
                transform: translateY(20px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        .animate-in {
            animation: fadeInUp 0.6s ease-out forwards;
        }

        .delay-1 {
            animation-delay: 0.1s;
        }

        .delay-2 {
            animation-delay: 0.2s;
        }

        .delay-3 {
            animation-delay: 0.3s;
        }

/* ========= Multi-page additions ========= */
.logo a { color: inherit; display: flex; align-items: center; text-decoration: none; }

.page-header {
    padding: 9.5rem 0 3.5rem;
    text-align: center;
    background: linear-gradient(180deg, #eef2ff 0%, #f8fafc 100%);
}
.page-header h1 { font-size: 2.7rem; margin-bottom: 0.8rem; }
.page-header p { max-width: 780px; margin: 0 auto; color: var(--gray-dark); }

.explore-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 1.5rem;
}
.explore-card {
    display: block;
    background: white;
    border-radius: var(--radius-lg);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    transition: var(--transition);
    border-top: 4px solid var(--primary);
}
.explore-card:hover { transform: translateY(-6px); box-shadow: var(--shadow-xl); }
.explore-card .ec-icon { font-size: 2.2rem; line-height: 1; }
.explore-card h3 { margin: 0.8rem 0 0.5rem; font-size: 1.25rem; }
.explore-card p { font-size: 0.95rem; margin-bottom: 0.9rem; }
.explore-card .ec-go { font-weight: 600; color: var(--primary); }

/* ========= CUHK-X Challenge promo (amber accent) ========= */
.challenge-bar {
    position: sticky;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1100;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-wrap: wrap;
    gap: 0.5rem 1rem;
    padding: 0.55rem 1.25rem;
    background: linear-gradient(135deg, #f59e0b, #d97706);
    color: #fff;
    font-size: 0.92rem;
    font-weight: 600;
    text-align: center;
    box-shadow: 0 2px 10px rgba(217, 119, 6, 0.3);
}
.challenge-bar:hover { color: #fff; }
.challenge-bar-text { color: #fff; }
.challenge-bar-cta {
    color: #fff;
    background: rgba(0, 0, 0, 0.18);
    padding: 0.18rem 0.7rem;
    border-radius: 999px;
    white-space: nowrap;
    font-weight: 700;
}

/* The bar is pinned at the very top; the fixed navbar is offset below it by the
   bar's real height (--bar-h, kept in sync by an inline script so it also tracks
   the bar wrapping on narrow screens). Fallbacks keep it sane without JS. */
.challenge-bar ~ .navbar { top: var(--bar-h, 2.75rem); }
/* push the hero clear of both the pinned bar and the navbar */
.challenge-bar ~ .hero {
    padding-top: calc(var(--bar-h, 2.75rem) + 8.5rem);
}

/* nav pill amber override */
.nav-links a.nav-cta.nav-challenge {
    background: linear-gradient(135deg, #f59e0b, #d97706);
    box-shadow: 0 2px 10px rgba(217, 119, 6, 0.35);
}
.nav-links a.nav-cta.nav-challenge:hover {
    box-shadow: 0 4px 14px rgba(217, 119, 6, 0.5);
}

/* hero spotlight card */
.challenge-spotlight {
    max-width: 760px;
    margin: 2.5rem auto 0;
    padding: 2rem 2.25rem;
    text-align: center;
    background: linear-gradient(160deg, #fffbeb 0%, #fff7ed 100%);
    border: 1px solid #fcd34d;
    border-radius: var(--radius-lg);
    box-shadow: 0 10px 30px rgba(217, 119, 6, 0.12);
}
.challenge-spotlight h3 {
    font-size: 1.5rem;
    margin-bottom: 0.4rem;
    color: #b45309;
}
.challenge-spotlight .cs-subtitle {
    font-size: 1rem;
    color: var(--gray-dark);
    margin-bottom: 1.25rem;
}
.challenge-spotlight .cs-stats {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.5rem 1.1rem;
    margin-bottom: 0.9rem;
    font-weight: 700;
    color: #92400e;
    font-size: 1.02rem;
}
.challenge-spotlight .cs-stats span { white-space: nowrap; }
.challenge-spotlight .cs-stats span + span::before {
    content: '·';
    margin-right: 1.1rem;
    color: #d97706;
}
.challenge-spotlight .cs-timeline {
    font-size: 0.92rem;
    color: var(--gray-dark);
    margin-bottom: 1.5rem;
}
.challenge-spotlight .cs-buttons {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 1rem;
}
.challenge-spotlight .btn-challenge {
    background: linear-gradient(135deg, #f59e0b 0%, #d97706 100%);
    color: #fff;
    box-shadow: 0 4px 14px rgba(217, 119, 6, 0.3);
}
.challenge-spotlight .btn-challenge:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(217, 119, 6, 0.45);
    color: #fff;
}
.challenge-spotlight .btn-challenge-outline {
    background: #fff;
    color: #b45309;
    border: 1px solid #f59e0b;
}
.challenge-spotlight .btn-challenge-outline:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
    color: #b45309;
}

@media (max-width: 700px) {
    .challenge-bar { font-size: 0.82rem; padding: 0.5rem 0.9rem; }
    .challenge-spotlight { padding: 1.5rem 1.25rem; }
    .challenge-spotlight .cs-buttons { flex-direction: column; align-items: center; }
    .challenge-spotlight .btn-challenge,
    .challenge-spotlight .btn-challenge-outline { width: 100%; max-width: 300px; }
}

/* mobile slide-down menu opens below the pinned bar + navbar */
@media (max-width: 768px) {
    .challenge-bar ~ .navbar .nav-links {
        top: calc(var(--bar-h, 2.75rem) + var(--nav-h, 64px));
    }
}