/* === Hengzhe's Science Classroom — Hub Styles === */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;600&display=swap');

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

:root {
    --bg-primary: #0a0a0f;
    --bg-secondary: #12121a;
    --bg-card: rgba(255,255,255,0.03);
    --bg-card-hover: rgba(255,255,255,0.07);
    --glass: rgba(255,255,255,0.05);
    --glass-border: rgba(255,255,255,0.08);
    --text-primary: #e8e8ef;
    --text-secondary: #8888a0;
    --text-muted: #55556a;
    --accent-blue: #4f8fff;
    --accent-purple: #a855f7;
    --accent-cyan: #22d3ee;
    --accent-green: #34d399;
    --accent-orange: #fb923c;
    --accent-pink: #f472b6;
    --accent-red: #f87171;
    --accent-yellow: #fbbf24;
    --glow-blue: 0 0 40px rgba(79,143,255,0.15);
    --glow-purple: 0 0 40px rgba(168,85,247,0.15);
    --glow-cyan: 0 0 40px rgba(34,211,238,0.15);
    --glow-green: 0 0 40px rgba(52,211,153,0.15);
}

html { scroll-behavior: smooth; }

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    overflow-x: hidden;
    line-height: 1.6;
}

/* === Particle Canvas === */
#particle-canvas {
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    z-index: 0;
    pointer-events: none;
}

/* === Navigation === */
.nav {
    position: fixed;
    top: 0; left: 0; right: 0;
    z-index: 100;
    padding: 16px 40px;
    display: flex;
    justify-content: center;
    align-items: center;
    backdrop-filter: blur(20px);
    background: rgba(10,10,15,0.7);
    border-bottom: 1px solid var(--glass-border);
    transition: all 0.3s ease;
}
.nav.scrolled {
    padding: 12px 40px;
    background: rgba(10,10,15,0.9);
}
.nav-links { display: flex; gap: 32px; }
.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 14px;
    font-weight: 500;
    transition: color 0.3s;
    position: relative;
}
.nav-links a:hover { color: var(--text-primary); }
.nav-links a::after {
    content: '';
    position: absolute;
    bottom: -4px; left: 0;
    width: 0; height: 2px;
    background: linear-gradient(90deg, var(--accent-blue), var(--accent-purple));
    border-radius: 1px;
    transition: width 0.3s ease;
}
.nav-links a:hover::after { width: 100%; }

/* === Hero === */
.hero {
    position: relative;
    z-index: 1;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    padding: 140px 40px 80px;
}
.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 8px 20px;
    border-radius: 100px;
    background: var(--glass);
    border: 1px solid var(--glass-border);
    font-size: 13px;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 32px;
    backdrop-filter: blur(10px);
    animation: fadeInUp 0.8s ease forwards;
    opacity: 0;
}
.hero-badge .pulse {
    width: 8px; height: 8px;
    border-radius: 50%;
    background: var(--accent-green);
    animation: pulse 2s ease-in-out infinite;
}
@keyframes pulse {
    0%, 100% { opacity: 1; transform: scale(1); }
    50% { opacity: 0.5; transform: scale(1.3); }
}
.hero h1 {
    font-size: clamp(48px, 8vw, 96px);
    font-weight: 900;
    line-height: 1.05;
    letter-spacing: -0.04em;
    margin-bottom: 24px;
    animation: fadeInUp 0.8s ease 0.15s forwards;
    opacity: 0;
}
.hero h1 .gradient-text {
    background: linear-gradient(135deg, var(--accent-blue) 0%, var(--accent-purple) 40%, var(--accent-pink) 70%, var(--accent-cyan) 100%);
    background-size: 200% auto;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    animation: gradientShift 6s ease infinite;
}
@keyframes gradientShift {
    0% { background-position: 0% center; }
    50% { background-position: 100% center; }
    100% { background-position: 0% center; }
}
.hero-subtitle {
    font-size: clamp(18px, 2.5vw, 24px);
    color: var(--text-secondary);
    max-width: 640px;
    font-weight: 400;
    line-height: 1.5;
    margin-bottom: 48px;
    animation: fadeInUp 0.8s ease 0.3s forwards;
    opacity: 0;
}
.hero-cta {
    display: flex;
    gap: 16px;
    animation: fadeInUp 0.8s ease 0.45s forwards;
    opacity: 0;
}
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 14px 28px;
    border-radius: 12px;
    font-size: 15px;
    font-weight: 600;
    text-decoration: none;
    transition: all 0.3s ease;
    cursor: pointer;
    border: none;
}
.btn-primary {
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    color: white;
    box-shadow: 0 4px 24px rgba(79,143,255,0.3);
}
.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 32px rgba(79,143,255,0.4);
}
.btn-secondary {
    background: var(--glass);
    color: var(--text-primary);
    border: 1px solid var(--glass-border);
    backdrop-filter: blur(10px);
}
.btn-secondary:hover {
    background: var(--bg-card-hover);
    border-color: rgba(255,255,255,0.15);
    transform: translateY(-2px);
}

/* === Stats Bar === */
.stats-bar {
    position: relative;
    z-index: 1;
    display: flex;
    justify-content: center;
    gap: 64px;
    padding: 48px 40px;
    border-top: 1px solid var(--glass-border);
    border-bottom: 1px solid var(--glass-border);
    background: var(--glass);
    backdrop-filter: blur(20px);
}
.stats-bar-top {
    position: fixed;
    top: 52px;
    left: 0; right: 0;
    z-index: 99;
    padding: 14px 40px;
    gap: 48px;
    background: rgba(10,10,15,0.85);
    border-top: none;
}
.nav.scrolled ~ .stats-bar-top,
.stats-bar-top.scrolled {
    padding: 10px 40px;
}
.stats-bar-top .stat-value {
    font-size: 22px;
}
.stats-bar-top .stat-label {
    font-size: 11px;
    margin-top: 2px;
}
.stat {
    text-align: center;
}
.stat-value {
    font-size: 42px;
    font-weight: 800;
    font-family: 'JetBrains Mono', monospace;
    letter-spacing: -0.03em;
    background: linear-gradient(135deg, var(--accent-cyan), var(--accent-blue));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}
.stat-label {
    font-size: 14px;
    color: var(--text-muted);
    font-weight: 500;
    margin-top: 4px;
}

/* === Section === */
.section {
    position: relative;
    z-index: 1;
    padding: 120px 40px;
    max-width: 1280px;
    margin: 0 auto;
}
.section-header {
    text-align: center;
    margin-bottom: 64px;
}
.section-tag {
    display: inline-block;
    font-size: 12px;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--accent-blue);
    margin-bottom: 16px;
}
.section-title {
    font-size: clamp(32px, 4vw, 48px);
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 16px;
}
.section-desc {
    font-size: 18px;
    color: var(--text-secondary);
    max-width: 560px;
    margin: 0 auto;
}

/* === Tier Layout === */
.tier {
    margin-bottom: 64px;
    position: relative;
}
.tier:last-child { margin-bottom: 0; }
.tier::before {
    content: '';
    position: absolute;
    left: 28px;
    top: 60px;
    bottom: -64px;
    width: 2px;
    background: linear-gradient(to bottom, var(--glass-border), transparent);
}
.tier:last-child::before { display: none; }

.tier-header {
    display: flex;
    align-items: center;
    gap: 20px;
    margin-bottom: 24px;
}
.tier-badge {
    flex-shrink: 0;
    width: 56px;
    height: 56px;
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 0.05em;
    z-index: 1;
}
.tier-foundation { background: rgba(52,211,153,0.15); color: var(--accent-green); border: 1px solid rgba(52,211,153,0.25); }
.tier-highschool { background: rgba(79,143,255,0.15); color: var(--accent-blue); border: 1px solid rgba(79,143,255,0.25); }
.tier-undergrad { background: rgba(168,85,247,0.15); color: var(--accent-purple); border: 1px solid rgba(168,85,247,0.25); }
.tier-graduate { background: rgba(251,146,60,0.15); color: var(--accent-orange); border: 1px solid rgba(251,146,60,0.25); }
.tier-frontier { background: rgba(244,114,182,0.15); color: var(--accent-pink); border: 1px solid rgba(244,114,182,0.25); }

.tier-info { flex: 1; }
.tier-name {
    font-size: 22px;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: 2px;
}
.tier-desc {
    font-size: 14px;
    color: var(--text-secondary);
}

.tier-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    margin-left: 76px;
}
.tier-grid-4 {
    grid-template-columns: repeat(2, 1fr);
}
.tier-grid-5 {
    grid-template-columns: repeat(2, 1fr);
}

/* === Discipline Grid === */
.discipline-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
    perspective: 1200px;
}
.discipline-card {
    position: relative;
    padding: 40px;
    border-radius: 20px;
    background: var(--bg-card);
    border: 1px solid var(--glass-border);
    overflow: hidden;
    transition: all 0.5s cubic-bezier(0.23, 1, 0.32, 1);
    cursor: default;
    opacity: 0;
    transform: translateY(40px);
}
.discipline-card.visible {
    opacity: 1;
    transform: translateY(0);
}
.discipline-card:hover {
    background: var(--bg-card-hover);
    border-color: rgba(255,255,255,0.12);
    transform: translateY(-4px);
}
.discipline-card::before {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0;
    height: 3px;
    border-radius: 20px 20px 0 0;
    opacity: 0;
    transition: opacity 0.5s ease;
}
.discipline-card:hover::before { opacity: 1; }
.discipline-card[data-color="blue"]::before { background: linear-gradient(90deg, var(--accent-blue), var(--accent-cyan)); }
.discipline-card[data-color="purple"]::before { background: linear-gradient(90deg, var(--accent-purple), var(--accent-pink)); }
.discipline-card[data-color="teal"]::before { background: linear-gradient(90deg, var(--accent-cyan), var(--accent-green)); }
.discipline-card[data-color="green"]::before { background: linear-gradient(90deg, var(--accent-green), var(--accent-cyan)); }
.discipline-card[data-color="orange"]::before { background: linear-gradient(90deg, var(--accent-orange), var(--accent-yellow)); }

.discipline-card:hover { box-shadow: var(--glow-blue); }
.discipline-card[data-color="purple"]:hover { box-shadow: var(--glow-purple); }
.discipline-card[data-color="teal"]:hover { box-shadow: var(--glow-cyan); }
.discipline-card[data-color="green"]:hover { box-shadow: var(--glow-green); }
.discipline-card[data-color="orange"]:hover { box-shadow: 0 0 40px rgba(251,146,60,0.15); }

.discipline-icon {
    width: 56px; height: 56px;
    border-radius: 14px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 28px;
    margin-bottom: 20px;
    position: relative;
}
.discipline-icon[data-color="blue"] { background: rgba(79,143,255,0.12); }
.discipline-icon[data-color="purple"] { background: rgba(168,85,247,0.12); }
.discipline-icon[data-color="teal"] { background: rgba(34,211,238,0.12); }
.discipline-icon[data-color="green"] { background: rgba(52,211,153,0.12); }
.discipline-icon[data-color="orange"] { background: rgba(251,146,60,0.12); }

.discipline-name {
    font-size: 24px;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: 8px;
}
.discipline-desc {
    font-size: 15px;
    color: var(--text-secondary);
    margin-bottom: 24px;
    line-height: 1.6;
}

/* === Textbook List === */
.textbook-list {
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.textbook-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 10px 14px;
    border-radius: 10px;
    background: rgba(255,255,255,0.02);
    border: 1px solid transparent;
    transition: all 0.3s ease;
    text-decoration: none;
    color: inherit;
}
.textbook-item:hover {
    background: rgba(255,255,255,0.05);
    border-color: var(--glass-border);
}
.textbook-emoji {
    font-size: 20px;
    flex-shrink: 0;
}
.textbook-info { flex: 1; min-width: 0; }
.textbook-title {
    font-size: 14px;
    font-weight: 600;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}
.textbook-author {
    font-size: 12px;
    color: var(--text-muted);
}
.textbook-status {
    font-size: 11px;
    font-weight: 600;
    padding: 4px 10px;
    border-radius: 100px;
    flex-shrink: 0;
}
.status-live {
    background: rgba(52,211,153,0.12);
    color: var(--accent-green);
}
.status-planned {
    background: rgba(136,136,160,0.12);
    color: var(--text-secondary);
}

/* === Features === */
.features-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}
.feature-card {
    padding: 32px;
    border-radius: 16px;
    background: var(--bg-card);
    border: 1px solid var(--glass-border);
    transition: all 0.4s ease;
    opacity: 0;
    transform: translateY(30px);
}
.feature-card.visible {
    opacity: 1;
    transform: translateY(0);
}
.feature-card:hover {
    background: var(--bg-card-hover);
    transform: translateY(-2px);
}
.feature-icon {
    font-size: 32px;
    margin-bottom: 16px;
}
.feature-title {
    font-size: 17px;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.01em;
}
.feature-desc {
    font-size: 14px;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* === Orbit Diagram === */
.orbit-section {
    position: relative;
    z-index: 1;
    padding: 120px 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
}
.orbit-container {
    position: relative;
    width: 500px;
    height: 500px;
}
.orbit-center {
    position: absolute;
    top: 50%; left: 50%;
    transform: translate(-50%, -50%);
    width: 100px; height: 100px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 14px;
    font-weight: 700;
    color: white;
    text-align: center;
    box-shadow: 0 0 60px rgba(79,143,255,0.3), 0 0 120px rgba(168,85,247,0.15);
    z-index: 2;
}
.orbit-ring {
    position: absolute;
    top: 50%; left: 50%;
    border-radius: 50%;
    border: 1px solid rgba(255,255,255,0.06);
}
.orbit-ring-1 { width: 250px; height: 250px; margin: -125px 0 0 -125px; }
.orbit-ring-2 { width: 380px; height: 380px; margin: -190px 0 0 -190px; }
.orbit-ring-3 { width: 480px; height: 480px; margin: -240px 0 0 -240px; }

.orbit-node {
    position: absolute;
    width: 48px; height: 48px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 22px;
    z-index: 3;
    cursor: default;
    transition: transform 0.3s ease;
}
.orbit-node:hover { transform: scale(1.2); }
.orbit-node[data-color="blue"] { background: rgba(79,143,255,0.2); border: 1px solid rgba(79,143,255,0.3); }
.orbit-node[data-color="purple"] { background: rgba(168,85,247,0.2); border: 1px solid rgba(168,85,247,0.3); }
.orbit-node[data-color="teal"] { background: rgba(34,211,238,0.2); border: 1px solid rgba(34,211,238,0.3); }
.orbit-node[data-color="green"] { background: rgba(52,211,153,0.2); border: 1px solid rgba(52,211,153,0.3); }
.orbit-node[data-color="orange"] { background: rgba(251,146,60,0.2); border: 1px solid rgba(251,146,60,0.3); }
.orbit-node[data-color="cyan"] { background: rgba(34,211,238,0.2); border: 1px solid rgba(34,211,238,0.3); }
.orbit-node[data-color="pink"] { background: rgba(244,114,182,0.2); border: 1px solid rgba(244,114,182,0.3); }

.orbit-label {
    position: absolute;
    font-size: 11px;
    font-weight: 600;
    color: var(--text-secondary);
    white-space: nowrap;
    pointer-events: none;
}

/* === Footer === */
.footer {
    position: relative;
    z-index: 1;
    text-align: center;
    padding: 48px 40px;
    border-top: 1px solid var(--glass-border);
    color: var(--text-muted);
    font-size: 14px;
}
.footer a {
    color: var(--accent-blue);
    text-decoration: none;
}
.footer a:hover { text-decoration: underline; }
.footer-license { font-size: 0.75rem; color: var(--text-muted, #666); margin-top: 8px; }

/* === Animations === */
@keyframes fadeInUp {
    from { opacity: 0; transform: translateY(24px); }
    to { opacity: 1; transform: translateY(0); }
}

@keyframes float {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}

/* Orbit rotation */
@keyframes orbitSpin1 { from { transform: rotate(0deg); } to { transform: rotate(360deg); } }
@keyframes orbitSpin2 { from { transform: rotate(60deg); } to { transform: rotate(420deg); } }
@keyframes orbitSpin3 { from { transform: rotate(120deg); } to { transform: rotate(480deg); } }

.orbit-ring-1 { animation: orbitSpin1 30s linear infinite; }
.orbit-ring-2 { animation: orbitSpin2 45s linear infinite; }
.orbit-ring-3 { animation: orbitSpin3 60s linear infinite; }

/* Counter-rotate nodes so they stay upright */
.orbit-ring-1 .orbit-node { animation: orbitSpin1 30s linear infinite reverse; }
.orbit-ring-2 .orbit-node { animation: orbitSpin2 45s linear infinite reverse; }
.orbit-ring-3 .orbit-node { animation: orbitSpin3 60s linear infinite reverse; }

/* === Language Toggle === */
.lang-toggle {
    font-size: 13px;
    padding: 6px 16px;
    border-radius: 100px;
    color: var(--text-secondary);
    background: var(--glass);
    border: 1px solid var(--glass-border);
    backdrop-filter: blur(10px);
    cursor: pointer;
    transition: all 0.3s ease;
    font-family: inherit;
    font-weight: 500;
}
.lang-toggle:hover {
    color: var(--text-primary);
    background: var(--bg-card-hover);
    box-shadow: 0 0 20px rgba(255,255,255,0.05);
}

/* === Responsive === */
@media (max-width: 1024px) {
    .tier-grid { grid-template-columns: repeat(2, 1fr); margin-left: 0; }
    .tier-grid-4 { grid-template-columns: repeat(2, 1fr); }
    .tier-grid-5 { grid-template-columns: repeat(2, 1fr); }
    .tier::before { display: none; }
    .discipline-grid { grid-template-columns: 1fr; }
    .features-grid { grid-template-columns: repeat(2, 1fr); }
    .stats-bar { gap: 40px; flex-wrap: wrap; }
    .orbit-container { width: 360px; height: 360px; }
    .orbit-ring-1 { width: 180px; height: 180px; margin: -90px 0 0 -90px; }
    .orbit-ring-2 { width: 280px; height: 280px; margin: -140px 0 0 -140px; }
    .orbit-ring-3 { width: 350px; height: 350px; margin: -175px 0 0 -175px; }
}
@media (max-width: 768px) {
    .nav { padding: 12px 20px; }
    .nav-links { gap: 20px; }
    .hero { padding: 100px 24px 60px; }
    .hero-cta { flex-direction: column; align-items: center; }
    .section { padding: 80px 24px; }
    .tier-grid { grid-template-columns: 1fr; margin-left: 0; }
    .tier-grid-4 { grid-template-columns: 1fr; }
    .tier-grid-5 { grid-template-columns: 1fr; }
    .tier-header { gap: 12px; }
    .tier-badge { width: 44px; height: 44px; font-size: 10px; border-radius: 12px; }
    .tier-name { font-size: 18px; }
    .features-grid { grid-template-columns: 1fr; }
    .stats-bar { gap: 24px; padding: 32px 20px; }
    .stats-bar-top { padding: 10px 16px; gap: 20px; top: 48px; }
    .stats-bar-top .stat-value { font-size: 18px; }
    .stats-bar-top .stat-label { font-size: 10px; }
    .stat-value { font-size: 32px; }
    .orbit-container { width: 300px; height: 300px; }
    .orbit-center { width: 70px; height: 70px; font-size: 11px; }
    .orbit-ring-1 { width: 150px; height: 150px; margin: -75px 0 0 -75px; }
    .orbit-ring-2 { width: 230px; height: 230px; margin: -115px 0 0 -115px; }
    .orbit-ring-3 { width: 290px; height: 290px; margin: -145px 0 0 -145px; }
    .orbit-node { width: 36px; height: 36px; font-size: 16px; }
}