/* ==========================================================================
   Frontiers of Physical Chemistry 2026 (SNBNCBS, Kolkata)
   Main Stylesheet - Design System & Layout
   ========================================================================== */

:root {
  /* Color Palette - Academic Navy & Modern Emerald / Amber */
  --primary-900: #071326;
  --primary-800: #0b1d3a;
  --primary-700: #102a54;
  --primary-600: #1e3a8a;
  --primary-500: #2563eb;
  
  --accent-teal: #0d9488;
  --accent-teal-light: #14b8a6;
  --accent-teal-dark: #0f766e;
  --accent-gold: #d97706;
  --accent-gold-light: #f59e0b;
  --accent-gold-hover: #b45309;

  --bg-main: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-alt: #f1f5f9;
  --bg-dark: #071326;
  --bg-dark-card: #0e2246;

  --text-main: #1e293b;
  --text-muted: #475569;
  --text-subtle: #64748b;
  --text-light: #f8fafc;
  --text-white: #ffffff;

  --border-light: #e2e8f0;
  --border-dark: rgba(255, 255, 255, 0.12);
  --border-gold: rgba(217, 119, 6, 0.4);

  /* Shadows & Glassmorphism */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -2px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.05);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.12), 0 8px 10px -6px rgba(0, 0, 0, 0.04);
  --shadow-glow: 0 0 25px rgba(13, 148, 136, 0.25);
  
  --glass-bg: rgba(255, 255, 255, 0.9);
  --glass-border: rgba(255, 255, 255, 0.5);
  --glass-blur: blur(12px);

  /* Typography */
  --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-heading: 'Outfit', var(--font-sans);
  
  /* Layout Transitions */
  --transition-fast: 0.18s ease;
  --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;
  
  --container-max: 1240px;
  --header-height: 80px;
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + 20px);
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  color: var(--text-main);
  background-color: var(--bg-main);
  line-height: 1.65;
  font-size: 1rem;
  overflow-x: hidden;
}

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

a {
  color: var(--primary-600);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-teal);
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  color: var(--primary-900);
  line-height: 1.25;
  font-weight: 700;
}

p {
  margin-bottom: 1rem;
}

p:last-child {
  margin-bottom: 0;
}

ul, ol {
  list-style-position: inside;
}

/* Container */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: 1.5rem;
  padding-right: 1.5rem;
}

/* Section Spacing & Headers */
.section {
  padding: 5rem 0;
  position: relative;
}

.section-alt {
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-light);
  border-bottom: 1px solid var(--border-light);
}

.section-dark {
  background-color: var(--primary-900);
  color: var(--text-light);
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}

.section-dark h1, 
.section-dark h2, 
.section-dark h3, 
.section-dark h4 {
  color: var(--text-white);
}

.section-header {
  text-align: center;
  max-width: 820px;
  margin: 0 auto 3.5rem auto;
}

.section-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.35rem 1rem;
  border-radius: var(--radius-full);
  background-color: rgba(13, 148, 136, 0.1);
  color: var(--accent-teal-dark);
  font-size: 0.825rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 1rem;
  border: 1px solid rgba(13, 148, 136, 0.25);
}

.section-dark .section-badge {
  background-color: rgba(20, 184, 166, 0.15);
  color: var(--accent-teal-light);
  border-color: rgba(20, 184, 166, 0.3);
}

.section-title {
  font-size: 2.25rem;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
}

@media (min-width: 768px) {
  .section-title {
    font-size: 2.75rem;
  }
}

.section-desc {
  font-size: 1.125rem;
  color: var(--text-muted);
  line-height: 1.7;
}

.section-dark .section-desc {
  color: #94a3b8;
}

/* ==========================================================================
   Header & Navigation
   ========================================================================== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border-bottom: 1px solid var(--border-light);
  z-index: 1000;
  transition: all var(--transition-normal);
}

.site-header.scrolled {
  background: rgba(7, 19, 38, 0.96);
  border-bottom-color: rgba(255, 255, 255, 0.1);
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.3);
}

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

.brand-wrapper {
  display: flex;
  align-items: center;
  gap: 0.875rem;
  text-decoration: none;
}

.brand-logos-group {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.brand-logo {
  height: 44px;
  width: 44px;
  border-radius: 50%;
  object-fit: cover;
  border: 2px solid var(--accent-gold);
  box-shadow: var(--shadow-sm);
  background: #ffffff;
}

.brand-logo-snb {
  height: 44px;
  width: auto;
  border-radius: 4px;
  background: #ffffff;
  border: 1.5px solid var(--accent-teal);
  padding: 1px 3px;
  object-fit: contain;
}

.brand-text {
  display: flex;
  flex-direction: column;
}

.brand-title {
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 1.15rem;
  color: var(--primary-900);
  line-height: 1.15;
  letter-spacing: -0.01em;
  transition: color var(--transition-fast);
}

.site-header.scrolled .brand-title {
  color: var(--text-white);
}

.brand-subtitle {
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--accent-teal);
  letter-spacing: 0.02em;
}

/* Nav Menu */
.nav-menu {
  display: none;
  align-items: center;
  gap: 1.25rem;
  list-style: none;
}

@media (min-width: 1024px) {
  .nav-menu {
    display: flex;
  }
}

.nav-link {
  font-size: 0.925rem;
  font-weight: 500;
  color: var(--text-main);
  padding: 0.4rem 0.25rem;
  position: relative;
  transition: color var(--transition-fast);
}

.site-header.scrolled .nav-link {
  color: #cbd5e1;
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background-color: var(--accent-gold);
  transition: width var(--transition-normal);
  border-radius: var(--radius-full);
}

.nav-link:hover,
.nav-link.active {
  color: var(--accent-teal-dark);
}

.site-header.scrolled .nav-link:hover,
.site-header.scrolled .nav-link.active {
  color: var(--accent-gold-light);
}

.nav-link:hover::after,
.nav-link.active::after {
  width: 100%;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
}

/* Mobile Toggle */
.mobile-toggle {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 42px;
  height: 42px;
  background: transparent;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  cursor: pointer;
  padding: 8px;
  gap: 5px;
  transition: all var(--transition-fast);
}

.site-header.scrolled .mobile-toggle {
  border-color: rgba(255, 255, 255, 0.2);
}

.mobile-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background-color: var(--primary-900);
  border-radius: 2px;
  transition: transform var(--transition-normal), opacity var(--transition-normal);
}

.site-header.scrolled .mobile-toggle span {
  background-color: var(--text-white);
}

.mobile-toggle.open span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.mobile-toggle.open span:nth-child(2) {
  opacity: 0;
}

.mobile-toggle.open span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

@media (min-width: 1024px) {
  .mobile-toggle {
    display: none;
  }
}

/* Mobile Drawer */
.mobile-drawer {
  position: fixed;
  top: var(--header-height);
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(7, 19, 38, 0.98);
  backdrop-filter: blur(16px);
  padding: 2rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  transform: translateY(-120%);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-normal);
  z-index: 999;
  overflow-y: auto;
}

.mobile-drawer.open {
  transform: translateY(0);
  opacity: 1;
  visibility: visible;
}

.mobile-nav-link {
  font-family: var(--font-heading);
  font-size: 1.25rem;
  font-weight: 600;
  color: #e2e8f0;
  padding: 0.6rem 0;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
}

.mobile-nav-link:hover,
.mobile-nav-link.active {
  color: var(--accent-gold-light);
  padding-left: 0.5rem;
}

/* ==========================================================================
   Simplified & Clean Hero Section
   ========================================================================== */
.hero-section {
  position: relative;
  min-height: 100vh;
  padding-top: calc(var(--header-height) + 1.5rem);
  padding-bottom: 5rem;
  display: flex;
  align-items: center;
  background: #071326;
  color: var(--text-white);
  overflow: hidden;
}

.hero-bg-overlay {
  position: absolute;
  inset: 0;
  background-image: linear-gradient(90deg, rgba(7, 19, 38, 0.96) 0%, rgba(7, 19, 38, 0.88) 45%, rgba(7, 19, 38, 0.4) 100%), 
                    url('../images/physchem-hero-banner.jpg');
  background-size: cover;
  background-position: right center;
  background-repeat: no-repeat;
  opacity: 0.95;
  z-index: 1;
}

.hero-particles {
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 10% 20%, rgba(13, 148, 136, 0.12) 0%, transparent 40%),
              radial-gradient(circle at 80% 80%, rgba(245, 158, 11, 0.08) 0%, transparent 40%);
  z-index: 2;
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 3;
  width: 100%;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2.5rem;
  align-items: center;
}

@media (min-width: 1024px) {
  .hero-grid {
    grid-template-columns: 1.2fr 0.8fr;
    gap: 3.5rem;
  }
}

/* Dual Logo Header in Hero */
.hero-logos-showcase {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  margin-bottom: 1.5rem;
  background: rgba(14, 34, 70, 0.7);
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: var(--radius-lg);
  padding: 0.75rem 1.25rem;
  backdrop-filter: blur(12px);
  width: fit-content;
}

.hero-logo-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.hero-logo-divider {
  width: 1px;
  height: 44px;
  background-color: rgba(255, 255, 255, 0.2);
}

.hero-logo-img {
  width: 52px;
  height: 52px;
  border-radius: 50%;
  object-fit: cover;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
  border: 2px solid var(--accent-gold);
  background: #ffffff;
  flex-shrink: 0;
}

.hero-logo-img.snb-logo {
  border-radius: 6px;
  width: auto;
  height: 52px;
  padding: 2px 4px;
  border: 2px solid var(--accent-teal);
  background: #ffffff;
  object-fit: contain;
}

.hero-logo-meta {
  display: flex;
  flex-direction: column;
}

.hero-logo-label {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-white);
  line-height: 1.2;
}

.hero-logo-sub {
  font-size: 0.725rem;
  color: var(--accent-teal-light);
  font-weight: 500;
}

.hero-title {
  font-size: 2.35rem;
  font-weight: 800;
  color: var(--text-white);
  line-height: 1.15;
  margin-bottom: 0.75rem;
  letter-spacing: -0.025em;
  text-shadow: 0 2px 10px rgba(0,0,0,0.5);
}

@media (min-width: 640px) {
  .hero-title {
    font-size: 2.85rem;
  }
}

@media (min-width: 1024px) {
  .hero-title {
    font-size: 3.25rem;
  }
}

.hero-title-highlight {
  background: linear-gradient(135deg, #fcd34d 0%, #f59e0b 50%, #14b8a6 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-subtitle {
  font-size: 1.3rem;
  font-weight: 600;
  color: var(--accent-teal-light);
  margin-bottom: 0.5rem;
  line-height: 1.3;
}

.hero-tagline {
  font-size: 1rem;
  color: #cbd5e1;
  margin-bottom: 1.75rem;
  font-style: italic;
}

.hero-meta-list {
  display: flex;
  flex-direction: column;
  gap: 0.875rem;
  margin-bottom: 2rem;
}

@media (min-width: 640px) {
  .hero-meta-list {
    flex-direction: row;
    flex-wrap: wrap;
    gap: 1.5rem;
  }
}

.hero-meta-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 1.05rem;
  color: #f1f5f9;
}

.hero-meta-icon {
  width: 22px;
  height: 22px;
  color: var(--accent-gold-light);
  flex-shrink: 0;
}

.hero-cta-group {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  align-items: center;
}

/* Hero Right: Interactive Card */
.hero-card {
  background: rgba(14, 34, 70, 0.82);
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: var(--radius-lg);
  padding: 2rem;
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4), var(--shadow-glow);
}

.hero-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.5rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.hero-card-title {
  font-size: 1.15rem;
  color: var(--text-white);
  font-weight: 700;
}

.hero-card-status {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8rem;
  color: #4ade80;
  font-weight: 600;
}

.pulse-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background-color: #4ade80;
  box-shadow: 0 0 0 0 rgba(74, 222, 128, 0.7);
  animation: pulse 1.8s infinite cubic-bezier(0.66, 0, 0, 1);
}

@keyframes pulse {
  to {
    box-shadow: 0 0 0 8px rgba(74, 222, 128, 0);
  }
}

/* ==========================================================================
   Footer
   ========================================================================== */
.site-footer {
  background-color: var(--primary-900);
  color: #94a3b8;
  padding: 4.5rem 0 2rem 0;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2.5rem;
  margin-bottom: 3.5rem;
}

@media (min-width: 640px) {
  .footer-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1024px) {
  .footer-grid {
    grid-template-columns: 1.5fr 1fr 1fr 1.2fr;
    gap: 3rem;
  }
}

.footer-col-title {
  color: var(--text-white);
  font-size: 1.1rem;
  font-weight: 700;
  margin-bottom: 1.25rem;
  letter-spacing: -0.01em;
  position: relative;
  padding-bottom: 0.5rem;
}

.footer-col-title::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 32px;
  height: 2px;
  background-color: var(--accent-gold);
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.footer-links a {
  color: #94a3b8;
  font-size: 0.925rem;
  transition: color var(--transition-fast), padding-left var(--transition-fast);
}

.footer-links a:hover {
  color: var(--accent-gold-light);
  padding-left: 0.25rem;
}

.footer-contact-item {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 0.875rem;
  font-size: 0.925rem;
  line-height: 1.5;
}

.footer-contact-icon {
  width: 18px;
  height: 18px;
  color: var(--accent-teal-light);
  flex-shrink: 0;
  margin-top: 3px;
}

.footer-bottom {
  padding-top: 2rem;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
  display: flex;
  flex-direction: column;
  gap: 1rem;
  align-items: center;
  text-align: center;
  font-size: 0.875rem;
}

@media (min-width: 768px) {
  .footer-bottom {
    flex-direction: row;
    justify-content: space-between;
    text-align: left;
  }
}

.back-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 44px;
  height: 44px;
  background-color: var(--accent-teal);
  color: #ffffff;
  border: none;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all var(--transition-normal);
  z-index: 900;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background-color: var(--accent-teal-dark);
  transform: translateY(-3px);
}