/* ============================================
   AISC 2026 — The AI Scientists Conference
   Color system: aiXiv blue primary palette
   ============================================ */

:root {
    --primary-50: #eff6ff;
    --primary-100: #dbeafe;
    --primary-200: #bfdbfe;
    --primary-300: #93c5fd;
    --primary-400: #60a5fa;
    --primary-500: #3b82f6;
    --primary-600: #2563eb;
    --primary-700: #1d4ed8;
    --primary-800: #1e40af;
    --primary-900: #1e3a8a;
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --accent-500: #8b5cf6;
    --accent-600: #7c3aed;
    --gray-50: #f9fafb;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-400: #9ca3af;
    --gray-500: #6b7280;
    --gray-600: #4b5563;
    --gray-700: #374151;
    --gray-800: #1f2937;
    --gray-900: #111827;
}

/* ---- Reset & Base ---- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    color: var(--gray-800);
    line-height: 1.6;
    background: #fff;
}

a { color: var(--primary-600); text-decoration: none; }
a:hover { color: var(--primary-700); }

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* ---- Navbar ---- */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid transparent;
    transition: all 0.3s ease;
}

.navbar.scrolled {
    border-bottom-color: var(--gray-200);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
}

.nav-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 700;
    font-size: 1.25rem;
    color: var(--gray-900);
}

.logo-icon { width: 28px; height: 28px; flex-shrink: 0; }

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

.nav-links a {
    color: var(--gray-600);
    font-size: 0.95rem;
    font-weight: 500;
    transition: color 0.2s;
}

.nav-links a:hover { color: var(--primary-600); }

.nav-submit-btn {
    background: var(--primary-600) !important;
    color: #fff !important;
    padding: 0.5rem 1.25rem;
    border-radius: 8px;
    font-weight: 600 !important;
    transition: background 0.2s !important;
}

.nav-submit-btn:hover {
    background: var(--primary-700) !important;
}

.mobile-menu-btn {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 4px;
}

.mobile-menu-btn span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--gray-700);
    border-radius: 2px;
    transition: all 0.3s;
}

.mobile-nav {
    display: none;
    flex-direction: column;
    padding: 1rem 1.5rem 1.5rem;
    gap: 1rem;
    border-top: 1px solid var(--gray-200);
}

.mobile-nav.open { display: flex; }

.mobile-nav a {
    color: var(--gray-700);
    font-weight: 500;
    padding: 0.5rem 0;
}

/* ---- Hero ---- */
.hero {
    padding: 10rem 0 6rem;
    text-align: center;
    background: linear-gradient(135deg, var(--primary-50) 0%, #fff 50%, var(--primary-50) 100%);
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -20%;
    width: 600px;
    height: 600px;
    background: radial-gradient(circle, var(--primary-100) 0%, transparent 70%);
    opacity: 0.5;
}

.hero-badge {
    display: inline-block;
    background: var(--primary-100);
    color: var(--primary-700);
    padding: 0.375rem 1rem;
    border-radius: 100px;
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    letter-spacing: 0.02em;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 800;
    color: var(--gray-900);
    margin-bottom: 0.5rem;
    letter-spacing: -0.02em;
    line-height: 1.1;
}

.hero-subtitle {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--primary-600);
    margin-bottom: 1.5rem;
}

.hero-description {
    font-size: 1.2rem;
    color: var(--gray-600);
    max-width: 700px;
    margin: 0 auto 2.5rem;
    line-height: 1.7;
}

.hero-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
    margin-bottom: 3rem;
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: 3rem;
    flex-wrap: wrap;
}

.stat {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.stat-icon { font-size: 1.25rem; }

.stat-label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--gray-700);
}

/* ---- Buttons ---- */
.btn {
    display: inline-flex;
    align-items: center;
    padding: 0.75rem 1.75rem;
    border-radius: 10px;
    font-weight: 600;
    font-size: 1rem;
    transition: all 0.2s ease;
    cursor: pointer;
    border: none;
}

.btn-primary {
    background: var(--primary-600);
    color: #fff;
    box-shadow: 0 2px 8px rgba(37, 99, 235, 0.25);
}

.btn-primary:hover {
    background: var(--primary-700);
    color: #fff;
    box-shadow: 0 4px 12px rgba(37, 99, 235, 0.35);
    transform: translateY(-1px);
}

.btn-secondary {
    background: #fff;
    color: var(--primary-600);
    border: 2px solid var(--primary-200);
}

.btn-secondary:hover {
    background: var(--primary-50);
    border-color: var(--primary-400);
    color: var(--primary-700);
}

.btn-lg {
    padding: 1rem 2.5rem;
    font-size: 1.1rem;
}

.btn-sm {
    padding: 0.5rem 1.1rem;
    font-size: 0.9rem;
    border-radius: 8px;
}

/* ---- Sections ---- */
.section {
    padding: 5rem 0;
}

.section-alt {
    background: var(--gray-50);
}

.section-title {
    font-size: 2.25rem;
    font-weight: 800;
    color: var(--gray-900);
    text-align: center;
    margin-bottom: 3rem;
    letter-spacing: -0.01em;
}

/* ---- About ---- */
.about-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 3rem;
    align-items: start;
}

.about-main p {
    margin-bottom: 1rem;
    font-size: 1.05rem;
    color: var(--gray-700);
    line-height: 1.8;
}

.about-cards {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1.25rem;
}

.feature-card {
    background: #fff;
    border: 1px solid var(--gray-200);
    border-radius: 12px;
    padding: 1.5rem;
    transition: all 0.2s ease;
}

.feature-card:hover {
    border-color: var(--primary-200);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.06);
    transform: translateY(-2px);
}

.feature-icon {
    font-size: 1.75rem;
    margin-bottom: 0.75rem;
}

.feature-card h3 {
    font-size: 1rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: 0.5rem;
}

.feature-card p {
    font-size: 0.875rem;
    color: var(--gray-500);
    line-height: 1.5;
}

/* ---- Call for Papers ---- */
.cfp-content {
    display: grid;
    grid-template-columns: 1.3fr 1fr;
    gap: 3rem;
    align-items: start;
}

.cfp-text h3 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--gray-900);
    margin: 2rem 0 1rem;
}

.cfp-text p {
    color: var(--gray-700);
    line-height: 1.7;
}

.topic-list, .guidelines-list {
    list-style: none;
    padding: 0;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.5rem;
    margin: 0.75rem 0;
}

.topic-list li, .guidelines-list li {
    padding: 0.375rem 0;
    padding-left: 1.5rem;
    position: relative;
    color: var(--gray-700);
    font-size: 0.95rem;
}

.topic-list li::before {
    content: '•';
    position: absolute;
    left: 0.25rem;
    color: var(--primary-500);
    font-weight: bold;
}

.guidelines-list {
    grid-template-columns: 1fr;
}

.guidelines-list li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--primary-500);
    font-weight: bold;
}

.submit-card {
    background: #fff;
    border: 2px solid var(--primary-200);
    border-radius: 16px;
    padding: 2.5rem;
    text-align: center;
    position: sticky;
    top: 6rem;
}

.submit-card h3 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: 1rem;
}

.submit-card p {
    color: var(--gray-600);
    margin-bottom: 1.5rem;
    line-height: 1.6;
}

.submit-note {
    font-size: 0.8rem;
    color: var(--gray-400);
    margin-top: 1rem !important;
    margin-bottom: 0 !important;
}

/* ---- Timeline ---- */
.timeline {
    max-width: 600px;
    margin: 0 auto;
    position: relative;
    padding-left: 2rem;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 11px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--gray-200);
}

.timeline-item {
    position: relative;
    padding: 0 0 2.5rem 2rem;
}

.timeline-item:last-child { padding-bottom: 0; }

.timeline-marker {
    position: absolute;
    left: -2rem;
    top: 0.25rem;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: #fff;
    border: 3px solid var(--gray-300);
    z-index: 1;
}

.timeline-marker.active {
    border-color: var(--primary-500);
    background: var(--primary-500);
    box-shadow: 0 0 0 4px var(--primary-100);
}

.timeline-date {
    font-size: 0.8rem;
    font-weight: 700;
    color: var(--primary-600);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 0.25rem;
}

.timeline-content h3 {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: 0.25rem;
}

.timeline-content p {
    color: var(--gray-500);
    font-size: 0.9rem;
}

/* ---- Organizers ---- */
.organizers-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    max-width: 800px;
    margin: 0 auto;
}

.organizer-card {
    text-align: center;
    padding: 2rem 1.5rem;
    background: #fff;
    border: 1px solid var(--gray-200);
    border-radius: 12px;
    transition: all 0.2s;
}

.organizer-card:hover {
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.06);
}

.placeholder-card {
    border-style: dashed;
    opacity: 0.7;
}

.organizer-avatar {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.organizer-card h3 {
    font-size: 1.05rem;
    font-weight: 700;
    color: var(--gray-800);
    margin-bottom: 0.25rem;
}

.organizer-role {
    font-size: 0.85rem;
    color: var(--primary-600);
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.organizer-affiliation {
    font-size: 0.85rem;
    color: var(--gray-400);
}

.student-coorg-wrap {
    max-width: 860px;
    margin: 0 auto;
}

.student-coorg-intro {
    color: var(--gray-600);
    line-height: 1.8;
    text-align: center;
    margin-bottom: 1.25rem;
}

/* student-coorg custom styles removed - now reusing organizer-card classes for consistency */

/* ---- Papers List ---- */
.papers-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    max-width: 800px;
    margin: 0 auto;
}

.paper-card {
    display: block;
    background: #fff;
    border: 1px solid var(--gray-200);
    border-radius: 10px;
    padding: 1.25rem 1.5rem;
    transition: all 0.2s ease;
    text-decoration: none;
    color: inherit;
}

.paper-card:hover {
    border-color: var(--primary-200);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
    transform: translateY(-1px);
}

.paper-meta {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
    flex-wrap: wrap;
}

.paper-badge {
    display: inline-block;
    padding: 0.125rem 0.5rem;
    border-radius: 100px;
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

.badge-paper { background: var(--primary-100); color: var(--primary-700); }
.badge-proposal { background: #fef3c7; color: #92400e; }
.badge-ai { background: #dbeafe; color: #1e40af; }
.badge-human { background: #d1fae5; color: #065f46; }
.badge-mixed { background: #ede9fe; color: #5b21b6; }

.paper-id {
    font-size: 0.75rem;
    color: var(--gray-400);
    font-family: monospace;
}

.paper-date {
    font-size: 0.75rem;
    color: var(--gray-400);
    margin-left: auto;
}

.paper-title {
    font-size: 1.05rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: 0.25rem;
    line-height: 1.4;
}

.paper-card:hover .paper-title {
    color: var(--primary-600);
}

.paper-authors {
    font-size: 0.85rem;
    color: var(--gray-500);
    margin-bottom: 0.25rem;
}

.paper-abstract {
    font-size: 0.8rem;
    color: var(--gray-400);
    line-height: 1.5;
    margin-top: 0.5rem;
}

/* ---- Footer ---- */
.footer {
    background: var(--gray-900);
    color: var(--gray-400);
    padding: 3rem 0 2rem;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--gray-700);
}

.footer-brand .logo-text {
    color: #fff;
    margin-left: 0.5rem;
}

.footer-brand p {
    color: var(--gray-400);
    font-size: 0.9rem;
    margin-top: 0.25rem;
}

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

.footer-links a {
    color: var(--gray-400);
    font-size: 0.9rem;
    transition: color 0.2s;
}

.footer-links a:hover {
    color: #fff;
}

.footer-bottom {
    text-align: center;
    padding-top: 1.5rem;
    font-size: 0.85rem;
}

.footer-bottom a {
    color: var(--primary-400);
}

/* ---- Responsive ---- */
@media (max-width: 900px) {
    .nav-links { display: none; }
    .mobile-menu-btn { display: flex; }

    .hero { padding: 8rem 0 4rem; }
    .hero-title { font-size: 2.5rem; }
    .hero-description { font-size: 1.05rem; }

    .about-grid { grid-template-columns: 1fr; }
    .about-cards { grid-template-columns: 1fr 1fr; }

    .cfp-content { grid-template-columns: 1fr; }
    .submit-card { position: static; }

    .topic-list { grid-template-columns: 1fr; }

    .organizers-grid { grid-template-columns: 1fr 1fr; }

    .footer-content { flex-direction: column; gap: 1.5rem; text-align: center; }
    .footer-links { flex-wrap: wrap; justify-content: center; }
}

@media (max-width: 600px) {
    .hero-title { font-size: 2rem; }
    .hero-actions { flex-direction: column; align-items: center; }
    .hero-stats { gap: 1.5rem; }

    .about-cards { grid-template-columns: 1fr; }

    .section-title { font-size: 1.75rem; }

    .organizers-grid { grid-template-columns: 1fr; max-width: 300px; }
}