/* ============================================
   Design System — Evolving Systems Lab @ WHU
   LIGHT THEME
   ============================================ */

/* System font stack — no external fonts required */

/* --- Custom Properties (Light) --- */
:root {
    /* palette */
    --bg-primary: #f8fafc;
    --bg-secondary: #ffffff;
    --bg-card: #ffffff;
    --bg-glass: rgba(255, 255, 255, 0.75);
    --border-light: #e2e8f0;
    --border-hover: #cbd5e1;

    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #94a3b8;

    --accent-blue: #3b82f6;
    --accent-cyan: #0891b2;
    --accent-purple: #7c3aed;
    --accent-pink: #ec4899;
    --accent-green: #059669;
    --accent-orange: #ea580c;

    --gradient-hero: linear-gradient(135deg, #eff6ff 0%, #f0f0ff 50%, #ecfdf5 100%);
    --gradient-accent: linear-gradient(135deg, var(--accent-blue), var(--accent-cyan));
    --gradient-purple: linear-gradient(135deg, var(--accent-purple), var(--accent-pink));
    --gradient-green: linear-gradient(135deg, var(--accent-green), var(--accent-cyan));

    /* spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;
    --space-4xl: 6rem;

    /* radius */
    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --radius-full: 9999px;

    /* shadows */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.1);
    --shadow-card: 0 1px 3px rgba(0, 0, 0, 0.04), 0 4px 12px rgba(0, 0, 0, 0.06);
    --shadow-glow-blue: 0 0 24px rgba(59, 130, 246, 0.12);
    --shadow-glow-purple: 0 0 24px rgba(124, 58, 237, 0.12);
    --shadow-glow-green: 0 0 24px rgba(5, 150, 105, 0.12);

    /* transition */
    --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);

    /* layout */
    --max-width: 1280px;
    --nav-height: 64px;
}

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

html {
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
}

img {
    max-width: 100%;
    display: block;
}

a {
    color: inherit;
    text-decoration: none;
}

button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    background: none;
}

/* --- Utility --- */
.container {
    max-width: var(--max-width) !important;
    margin: 0 auto !important;
    padding: 0 var(--space-xl) !important;
}

.section-title {
    font-size: 2rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-md);
    color: var(--text-primary);
}

.section-subtitle {
    font-size: 1.05rem;
    color: var(--text-secondary);
    max-width: 640px;
    line-height: 1.7;
}

.badge {
    display: inline-flex;
    align-items: center;
    gap: var(--space-xs);
    padding: var(--space-xs) var(--space-md);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.badge--blue {
    background: #dbeafe;
    color: #1d4ed8;
}

.badge--purple {
    background: #ede9fe;
    color: #6d28d9;
}

.badge--green {
    background: #d1fae5;
    color: #047857;
}

.badge--cyan {
    background: #cffafe;
    color: #0e7490;
}

.badge--orange {
    background: #ffedd5;
    color: #c2410c;
}

.badge--pink {
    background: #fce7f3;
    color: #be185d;
}

/* ==============================
   NAVIGATION
   ============================== */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    height: var(--nav-height);
    display: flex;
    align-items: center;
    background: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--border-light);
    transition: box-shadow var(--transition-base);
}

.navbar.scrolled {
    box-shadow: var(--shadow-sm);
}

.navbar .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 1.05rem;
    font-weight: 700;
    white-space: nowrap;
    color: var(--text-primary);
}

.nav-brand .logo-icon {
    width: 32px;
    height: 32px;
    background: var(--gradient-accent);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.9rem;
    flex-shrink: 0;
    color: #fff;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    list-style: none;
}

.nav-links a {
    font-size: 0.88rem;
    font-weight: 500;
    color: var(--text-secondary);
    padding: 0.4rem 0.85rem;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.nav-links a:hover {
    color: var(--text-primary);
    background: rgba(0, 0, 0, 0.04);
}

.nav-links a.active {
    color: var(--accent-blue);
    background: #eff6ff;
}

/* ==============================
   HERO (compact)
   ============================== */
.hero {
    position: relative;
    padding: calc(var(--nav-height) + var(--space-3xl)) 0 var(--space-3xl);
    background: var(--gradient-hero);
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -20%;
    width: 600px;
    height: 600px;
    border-radius: 50%;
    background: radial-gradient(circle, rgba(59, 130, 246, 0.08) 0%, transparent 70%);
    pointer-events: none;
}

.hero::after {
    content: '';
    position: absolute;
    bottom: -30%;
    left: -10%;
    width: 500px;
    height: 500px;
    border-radius: 50%;
    background: radial-gradient(circle, rgba(124, 58, 237, 0.06) 0%, transparent 70%);
    pointer-events: none;
}

.hero-layout {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-3xl);
    align-items: center;
    position: relative;
    z-index: 1;
}

.hero-content {
    max-width: 560px;
}

.hero-badge {
    margin-bottom: var(--space-lg);
}

.hero h1 {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 900;
    letter-spacing: -0.03em;
    line-height: 1.15;
    margin-bottom: var(--space-md);
    color: var(--text-primary);
}

.hero h1 .text-gradient {
    background: var(--gradient-accent);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero p {
    font-size: 1.05rem;
    color: var(--text-secondary);
    line-height: 1.75;
    margin-bottom: var(--space-xl);
}

.hero-actions {
    display: flex;
    gap: var(--space-md);
    flex-wrap: wrap;
}

.hero-highlights {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-md);
}

.highlight-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: var(--space-lg);
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-sm);
}

.highlight-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
    border-color: var(--border-hover);
}

.highlight-card .hl-icon {
    font-size: 1.5rem;
    margin-bottom: var(--space-sm);
}

.highlight-card h4 {
    font-size: 0.95rem;
    font-weight: 700;
    margin-bottom: var(--space-xs);
}

.highlight-card p {
    font-size: 0.82rem;
    color: var(--text-muted);
    line-height: 1.5;
    margin: 0;
}

/* --- Buttons --- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 0.7rem 1.5rem;
    border-radius: var(--radius-full);
    font-size: 0.9rem;
    font-weight: 600;
    transition: all var(--transition-fast);
}

.btn-primary {
    background: var(--gradient-accent);
    color: #fff;
    box-shadow: 0 2px 12px rgba(59, 130, 246, 0.25);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 20px rgba(59, 130, 246, 0.35);
}

.btn-secondary {
    background: #fff;
    color: var(--text-primary);
    border: 1px solid var(--border-light);
    box-shadow: var(--shadow-sm);
}

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

/* ==============================
   TAB NAVIGATION (Products)
   ============================== */
.products {
    padding: var(--space-4xl) 0;
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-light);
    border-bottom: 1px solid var(--border-light);
}

.products-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.tab-nav {
    display: flex;
    justify-content: center;
    gap: var(--space-xs);
    margin-top: var(--space-2xl);
    padding: 4px;
    background: var(--bg-primary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-full);
    width: fit-content;
    margin-left: auto;
    margin-right: auto;
}

.tab-btn {
    padding: 0.6rem 1.35rem;
    border-radius: var(--radius-full);
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
    white-space: nowrap;
}

.tab-btn:hover {
    color: var(--text-primary);
    background: #fff;
}

.tab-btn.active {
    color: #fff;
    background: var(--gradient-accent);
    box-shadow: 0 2px 8px rgba(59, 130, 246, 0.2);
}

.tab-btn[data-tab="psi"].active {
    background: var(--gradient-purple);
    box-shadow: 0 2px 8px rgba(124, 58, 237, 0.2);
}

.tab-btn[data-tab="embedded"].active {
    background: var(--gradient-green);
    box-shadow: 0 2px 8px rgba(5, 150, 105, 0.2);
}

/* --- Tab Panels --- */
.tab-panels {
    position: relative;
}

.tab-panel {
    display: none;
    animation: panelFadeIn var(--transition-base);
}

.tab-panel.active {
    display: block;
}

@keyframes panelFadeIn {
    from {
        opacity: 0;
        transform: translateY(12px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* --- Product Panel Layout --- */
.product-hero {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-3xl);
    align-items: center;
    margin-bottom: var(--space-3xl);
}

.product-info h3 {
    font-size: 1.6rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-md);
}

.product-info p {
    color: var(--text-secondary);
    font-size: 1rem;
    line-height: 1.75;
    margin-bottom: var(--space-xl);
}

.product-visual {
    aspect-ratio: 16 / 10;
    border-radius: var(--radius-lg);
    overflow: hidden;
    border: 1px solid var(--border-light);
    background: var(--bg-primary);
    box-shadow: var(--shadow-card);
}

.product-visual-inner {
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 4rem;
}

.product-visual-inner.blue {
    background: linear-gradient(135deg, #eff6ff, #e0f2fe);
}

.product-visual-inner.purple {
    background: linear-gradient(135deg, #f5f3ff, #fce7f3);
}

.product-visual-inner.green {
    background: linear-gradient(135deg, #ecfdf5, #e0f2fe);
}

/* --- Feature cards --- */
.features-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-lg);
}

.feature-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    transition: all var(--transition-base);
    position: relative;
    overflow: hidden;
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--gradient-accent);
    opacity: 0;
    transition: opacity var(--transition-fast);
}

.feature-card:hover {
    transform: translateY(-4px);
    border-color: var(--border-hover);
    box-shadow: var(--shadow-lg), var(--shadow-glow-blue);
}

.feature-card:hover::before {
    opacity: 1;
}

.feature-card.purple-glow:hover {
    box-shadow: var(--shadow-lg), var(--shadow-glow-purple);
}

.feature-card.purple-glow::before {
    background: var(--gradient-purple);
}

.feature-card.green-glow:hover {
    box-shadow: var(--shadow-lg), var(--shadow-glow-green);
}

.feature-card.green-glow::before {
    background: var(--gradient-green);
}

.feature-icon {
    width: 48px;
    height: 48px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
    margin-bottom: var(--space-lg);
}

.feature-icon.blue {
    background: #dbeafe;
}

.feature-icon.purple {
    background: #ede9fe;
}

.feature-icon.green {
    background: #d1fae5;
}

.feature-icon.cyan {
    background: #cffafe;
}

.feature-icon.orange {
    background: #ffedd5;
}

.feature-icon.pink {
    background: #fce7f3;
}

.feature-card h4 {
    font-size: 1.05rem;
    font-weight: 700;
    margin-bottom: var(--space-sm);
}

.feature-card p {
    color: var(--text-secondary);
    font-size: 0.88rem;
    line-height: 1.65;
}

/* ==============================
   RESEARCH PAPERS
   ============================== */
.papers {
    padding: var(--space-4xl) 0;
    background: var(--bg-primary);
}

.papers-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.papers-list {
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
    max-width: 900px;
    margin: 0 auto;
}

.paper-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: var(--space-lg) var(--space-xl);
    display: flex;
    gap: var(--space-lg);
    align-items: flex-start;
    transition: all var(--transition-fast);
}

.paper-card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--border-hover);
    transform: translateY(-2px);
}

.paper-year {
    font-size: 0.78rem;
    font-weight: 700;
    color: var(--accent-blue);
    background: #eff6ff;
    padding: 0.3rem 0.7rem;
    border-radius: var(--radius-full);
    white-space: nowrap;
    flex-shrink: 0;
    margin-top: 2px;
}

.paper-content h4 {
    font-size: 1rem;
    font-weight: 700;
    margin-bottom: var(--space-xs);
    line-height: 1.4;
}

.paper-content .paper-authors {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: var(--space-xs);
}

.paper-content .paper-venue {
    font-size: 0.82rem;
    color: var(--text-secondary);
    font-style: italic;
}

.paper-tags {
    display: flex;
    gap: var(--space-xs);
    margin-top: var(--space-sm);
    flex-wrap: wrap;
}

.paper-tag {
    font-size: 0.7rem;
    padding: 0.15rem 0.5rem;
    border-radius: var(--radius-full);
    font-weight: 600;
    background: #f1f5f9;
    color: var(--text-muted);
}

/* ==============================
   MEMBERS
   ============================== */
.members {
    padding: var(--space-4xl) 0;
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-light);
    border-bottom: 1px solid var(--border-light);
}

.members-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.members-group-title {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--text-secondary);
    margin-bottom: var(--space-lg);
    padding-bottom: var(--space-sm);
    border-bottom: 2px solid var(--border-light);
}

.members-group+.members-group {
    margin-top: var(--space-2xl);
}

.members-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: var(--space-lg);
}

.member-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    text-align: center;
    transition: all var(--transition-fast);
}

.member-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-md);
    border-color: var(--border-hover);
}

.member-avatar {
    width: 72px;
    height: 72px;
    border-radius: 50%;
    margin: 0 auto var(--space-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    background: linear-gradient(135deg, #dbeafe, #ede9fe);
}

.member-card h4 {
    font-size: 1rem;
    font-weight: 700;
    margin-bottom: var(--space-xs);
}

.member-card .member-role {
    font-size: 0.82rem;
    color: var(--text-muted);
    margin-bottom: var(--space-sm);
}

.member-card .member-focus {
    font-size: 0.78rem;
    color: var(--accent-blue);
    font-weight: 500;
}

/* ==============================
   CONTACT
   ============================== */
.contact {
    padding: var(--space-4xl) 0;
    background: var(--bg-primary);
}

.contact-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.contact-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-lg);
    max-width: 900px;
    margin: 0 auto;
}

.contact-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    text-align: center;
    transition: all var(--transition-fast);
}

.contact-card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--border-hover);
    transform: translateY(-2px);
}

.contact-icon {
    width: 56px;
    height: 56px;
    border-radius: var(--radius-md);
    margin: 0 auto var(--space-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    background: #eff6ff;
}

.contact-card h4 {
    font-size: 0.95rem;
    font-weight: 700;
    margin-bottom: var(--space-xs);
}

.contact-card p {
    font-size: 0.88rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.contact-card a {
    color: var(--accent-blue);
    font-weight: 500;
}

.contact-card a:hover {
    text-decoration: underline;
}

/* ==============================
   FOOTER
   ============================== */
.footer {
    padding: var(--space-2xl) 0 var(--space-lg);
    border-top: 1px solid var(--border-light);
    background: var(--bg-secondary);
}

.footer-bottom {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.footer-bottom p {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.footer-links {
    display: flex;
    gap: var(--space-lg);
    list-style: none;
}

.footer-links a {
    font-size: 0.82rem;
    color: var(--text-muted);
    transition: color var(--transition-fast);
}

.footer-links a:hover {
    color: var(--text-primary);
}

/* ==============================
   SCROLL ANIMATIONS
   ============================== */
.fade-in {
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in.visible {
    opacity: 1;
    transform: translateY(0);
}

/* ==============================
   RESPONSIVE
   ============================== */
@media (max-width: 968px) {
    .hero-layout {
        grid-template-columns: 1fr;
        gap: var(--space-2xl);
    }

    .hero-highlights {
        grid-template-columns: 1fr 1fr;
    }

    .product-hero {
        grid-template-columns: 1fr;
        gap: var(--space-2xl);
    }

    .features-grid {
        grid-template-columns: 1fr 1fr !important;
    }

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

    .footer-bottom {
        flex-direction: column;
        gap: var(--space-sm);
        text-align: center;
    }
}

@media (max-width: 768px) {
    :root {
        --nav-height: 56px;
    }

    .container {
        padding: 0 var(--space-md);
    }

    .nav-links {
        display: none;
    }

    .mobile-menu-btn {
        display: flex;
    }

    .hero {
        padding: calc(var(--nav-height) + var(--space-2xl)) 0 var(--space-2xl);
    }

    .hero h1 {
        font-size: 1.8rem;
    }

    .hero p {
        font-size: 0.95rem;
    }

    .hero-highlights {
        grid-template-columns: 1fr;
    }

    .section-title {
        font-size: 1.5rem;
    }

    .tab-nav {
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
        width: 100%;
        justify-content: flex-start;
        padding: 4px;
    }

    .tab-btn {
        font-size: 0.8rem;
        padding: 0.5rem 0.9rem;
    }

    .features-grid {
        grid-template-columns: 1fr !important;
    }

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

    .paper-card {
        flex-direction: column;
        gap: var(--space-sm);
    }

    .products,
    .papers,
    .members,
    .contact {
        padding: var(--space-3xl) 0;
    }
}

@media (max-width: 480px) {
    .hero-actions {
        flex-direction: column;
        align-items: stretch;
    }

    .btn {
        justify-content: center;
    }

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

    .footer-links {
        flex-direction: column;
        gap: var(--space-sm);
        align-items: center;
    }
}

/* Hamburger — hidden on desktop */
.mobile-menu-btn {
    display: none;
    flex-direction: column;
    gap: 5px;
    padding: 4px;
    cursor: pointer;
    z-index: 110;
}

.mobile-menu-btn span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: all var(--transition-fast);
}

/* Mobile nav overlay */
.mobile-nav {
    display: none;
    position: fixed;
    inset: 0;
    z-index: 99;
    background: rgba(255, 255, 255, 0.97);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: var(--space-xl);
}

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

.mobile-nav a {
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--text-secondary);
    transition: color var(--transition-fast);
}

.mobile-nav a:hover {
    color: var(--accent-blue);
}